RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, ISO 3506 SS grades, NACE MR0175 compliance, Third-Party Inspection, ISO / DIN / ASME standards, and complete EPC export documentation packages.
Dowel Pins
A world-class technical reference for EPC contractors, mechanical and precision engineers, procurement heads, TPI inspection agencies, and global project buyers specifying dowel pins in precision alignment, location, shear load transfer, and assembly indexing applications across Oil & Gas, Power Generation, Petrochemical, Hydraulic Systems, Precision Machinery, Tooling, and Industrial Manufacturing sectors worldwide.
Pin Type Classification
& Load Mechanics
Dowel pins are precision cylindrical fastening and locating elements installed in close-tolerance holes in mating components to provide accurate positional alignment, transfer shear loads between assembled parts, index components for repeatable disassembly and re-assembly to the same position, and prevent relative movement under service loads. They are fundamental components in hydraulic manifolds, valve bodies, precision machinery, tooling, and structural connections throughout EPC and industrial manufacturing.
1.1 — Technical Definition and Functional Role
A dowel pin is a precision-machined cylindrical pin — ground to a specific diameter tolerance class — pressed or slip-fitted into reamed or precision-bored holes in two or more mating components. Unlike threaded fasteners, which transfer load axially through thread engagement and bolt tension, dowel pins transfer load transversely (in shear) through the contact between the pin body and the bore wall of the mating components. This makes dowel pins uniquely suited to applications requiring precise component alignment, repeatable location, and shear load transfer without relying on fastener friction.
In EPC and precision engineering contexts, dowel pins appear in: hydraulic manifold sub-plate alignment and positional retention, valve body and actuator housing assembly, pump and compressor housing register alignment, gearbox and reducer housing cover location, precision jig and fixture component indexing, tooling die and mould component registration, equipment base frame alignment on foundation plates, coupling half register alignment for shaft coupling assemblies, linear guide carriage register location, and any assembly requiring repeatable component positioning to tolerances below what threaded fasteners alone can reliably achieve.
RR Hydraulic manufactures and supplies dowel pins under all applicable international standards with full EN 10204 3.1 / 3.2 material traceability and project documentation capability.
1.2 — Dowel Pin Type Classification
Solid Cylindrical Dowel — ISO 8734 (Hardened)
The standard precision dowel pin. Ground to h6 or m6 tolerance class (interference or transition fit with H7 reamed hole). Hardened carbon steel (case hardened 60+ HRC surface; hard alloy steel) or stainless steel. Per ISO 8734 (hardened and ground) and DIN 6325. Used in all precision alignment and shear transfer applications — hydraulic manifolds, tooling, precision machinery, and pump housings. The reference dowel pin type for EPC precision assembly.
Solid Cylindrical Dowel — ISO 8735 (Unhardened)
Same geometry as ISO 8734 but manufactured from unhardened steel — ground to h8 tolerance class (loose slip fit). Per ISO 8735. Used for non-precision location and shear transfer where the hole tolerance is less tight and press-fit retention is not required. Lower cost than hardened pins; suitable for structural alignment over precision instrument-grade alignment. Stainless steel version commonly used for marine and offshore assembly.
Spring (Roll / Hollow) Pin — ISO 8752 / DIN 1481
Hollow cylindrical pin manufactured from a coiled or rolled strip — the split along its length allows the pin to compress during installation, generating a radial spring force that retains it in the hole without press-fitting. Per ISO 8752 (standard duty) and ISO 13337 (light duty); also DIN 1481. Used where shock loads or vibration are present and the assembly must be easily disassembled. Accepts some hole tolerance variation — more forgiving than solid pins. Lower precision alignment capability.
Taper Pin — ISO 2339 / DIN 1 / DIN 7977
Conical pin with a 1:50 taper (1:50 = 0.02 mm diameter reduction per mm length). Driven into a tapered reamed hole; the taper creates a wedging self-locking action under axial insertion force. Per ISO 2339 (unhardened), DIN 7977 (threaded end for extraction), DIN 7 (metric). Used for hub-to-shaft keying, lever-to-shaft attachment, and removable connections requiring positive mechanical locking without press-fit tools. Threaded version (with nut on end) allows withdrawal without drift-pin hammering.
Grooved (Knurled) Pin — ISO 8740 / DIN 1474
Cylindrical pin with longitudinal grooves pressed into the body — the raised material at the groove edges displaces into the hole wall on installation, creating an interference retention without a precision reamed hole. Per ISO 8740 (parallel, full-length grooves) and DIN 1471–1474 (various groove patterns). Suitable for softer substrate materials (aluminium, brass, mild steel). Lower precision alignment than solid pins; simpler hole preparation (drill rather than ream).
Pull-Out Dowel (Threaded / Extraction) — DIN 7979
Solid cylindrical precision dowel with an internal thread at one or both ends, allowing extraction with a standard bolt or slide hammer attachment when the pin is press-fitted in a blind hole. Per DIN 7979 (metric internal thread) and DIN 7977 (taper pin with threaded shank). Essential for hydraulic manifold assembly and valve body assembly where press-fit dowels must be removed for maintenance without damaging the precision-reamed bore.
1.3 — Dowel Pin vs Bolt vs Key: Functional Comparison
| Parameter | Solid Dowel Pin | Bolt / SHCS | Woodruff Key | Roll / Spring Pin | Engineering Implication |
|---|---|---|---|---|---|
| Load transfer mode | Shear — transverse | Tension — axial preload friction | Shear — transverse (1 plane) | Shear — transverse | Dowel: highest shear precision transfer |
| Alignment precision | Highest (h6/m6 tolerance) | Poor — clearance bolt holes | Moderate (key slot tolerance) | Low — spring compliance | Dowel: required for precision component location |
| Hole preparation | Precision ream (H7) | Drill + tap or clearance | Broach/mill keyway | Drill only | Dowel: most demanding hole prep |
| Removability | Moderate (drift-pin or threaded extract) | Excellent | Good (drive out) | Good (drift-pin) | Blind holes: use threaded extraction dowel |
| Shock / vibration | Excellent — no loosening possible | Moderate — preload dependent | Good | Very Good (spring action) | Dowel: immune to vibration loosening |
| Repeatability | Excellent — µm level | Poor — bolt hole clearance | Moderate | Moderate | Dowel: precision re-assembly indexing |
| Cost | Moderate–High (precision machining) | Low | Low | Low | Dowel: cost justified by precision requirement |
1.4 — Load Characteristics and Failure Modes
Single-Shear Loading
The pin is loaded in shear across one cross-section — the shear plane coincides with the mating surface between the two joined components. Shear stress τ = F / A_s where A_s = π × d² / 4. The single-shear capacity = τ_ult × A_s = 0.577 × S_y × A_s (von Mises yield criterion). Single shear governs for dowels in lap joints, flange connections, and cover plate assemblies. Design load must not exceed 0.5 × shear yield capacity for a safety factor of 2:1.
Double-Shear Loading
The pin is supported at both ends and loaded at its mid-point — two shear planes develop simultaneously. Double-shear capacity = 2 × τ_ult × A_s — twice the single-shear capacity for the same pin diameter. Occurs in clevises, bifurcated joints, yoke-and-rod connections, and when the pin passes through three components with the centre component carrying the full applied load. The standard configuration for structural pin connections in pipe supports, equipment brackets, and lifting attachments.
Bearing Stress on Hole Wall
Shear force on the pin creates bearing pressure on the hole wall of the softer mating component. Bearing stress σ_b = F / (d × L_bearing) where L_bearing is the effective bearing length. Bearing failure — permanent deformation of the hole wall — is often the governing failure mode in aluminium housings and cast iron covers with hardened steel dowel pins. Verify bearing stress against 0.9 × S_y of the hole material, not the pin material.
Press-Fit Retention (Pull-Out)
Press-fitted dowel pins (h6/m6 tolerance in H7 hole) are retained by the interference fit pressure and friction between pin OD and hole bore. Pull-out force = π × d × L × p × μ where p is the contact pressure from interference and μ is the friction coefficient. For hydraulic manifold dowels: pull-out retention must exceed the maximum hydraulic reaction force on the sub-plate + dynamic pressure forces during valve actuation. Blind-hole press-fit dowels in critical assemblies: use threaded extraction version (DIN 7979) to enable maintenance access.
Fatigue at Shear Plane
Dowel pins in cyclic-load applications (rotating machinery registers, reciprocating pump housing covers, valve body covers in pulsating pressure service) are subject to fatigue fracture at the shear plane — the cross-section of minimum area under maximum stress. Hardened steel pins (ISO 8734) with smooth, ground surfaces provide better fatigue life than unhardened or grooved pins due to the absence of surface stress concentrations. For high-cycle fatigue applications, specify ISO 8734 hardened and ground pins with a surface finish Ra ≤ 0.4 µm.
Hole Tolerance and Fit Class Selection
The fit between the dowel pin and the reamed hole determines: location precision, assembly/disassembly force, and vibration retention. H7/h6 is a transition fit (slight press in most cases) — standard for precision location with periodic maintenance disassembly. H7/n6 is an interference fit — permanent or near-permanent assembly requiring press equipment for removal. H7/h8 is a slip fit — easy assembly/disassembly; used for alignment-only dowels where retention is provided by separate fasteners. Specify fit class on the engineering drawing, not just nominal pin diameter.
1.5 — Shear Capacity Calculation
τ_allow = Allowable shear stress = S_y / √3 (von Mises) with safety factor
S_y = Yield strength of pin material (MPa) — ISO 8734 hardened steel: typically 900–1200 MPa
d = Pin nominal diameter (mm)
A_s = Pin cross-sectional area = π × d² / 4 (mm²)
Double-shear capacity: F_double = 2 × F_shear
Bearing capacity check: F_bear = σ_b,allow × d × L_b
σ_b,allow = 0.9 × S_y of hole wall material; L_b = bearing length per component
Design safety factor: SF = 2.0–3.0 on yield shear strength for static loads;
SF = 3.0–5.0 for dynamic / fatigue loads
A_s = π × 8² / 4 = 50.27 mm²
S_y (hardened steel) = 1000 MPa (conservative estimate for ISO 8734 grade)
τ_allow = 1000 / (√3 × 2.0) = 288.7 MPa (SF = 2.0 on yield)
F_allow = 288.7 × 50.27 = 14,513 N = 14.5 kN per pin
Bearing check (aluminium housing, S_y = 270 MPa, L_b = 12 mm):
F_bear = 0.9 × 270 × 8 × 12 = 23,328 N = 23.3 kN — shear governs.
Submit your pin type, diameter, length, tolerance class, material, finish, and quantity for a documented RFQ within 24 hours.
Tolerance Classes &
Standards Compliance
Dowel pin dimensions — nominal diameter, length, diameter tolerance class, chamfer, and surface finish — are governed by ISO 8734 (hardened), ISO 8735 (unhardened), DIN 6325, and ASME B18.8.2 (inch). Tolerance class selection determines the fit with the mating reamed hole and therefore the assembly precision and retention force. All applicable standards are supported with full certification at RR Hydraulic.
Submit pin type, diameter, tolerance class, length, material, and quantity to sales@rrhydraulics.com for a fully certified offer.
2.1 — ISO 8734 Hardened Cylindrical Dowel Pin Dimensional Table
| Nominal Dia d (mm) | Tolerance Class | Max Dia (mm) | Min Dia (mm) | Chamfer c (mm) | Surface Finish Ra (µm) | Standard Lengths L (mm) | Matching Hole (H7) | Cross-Section Area (mm²) |
|---|---|---|---|---|---|---|---|---|
| 1.0 | h6 | 1.000 | 0.994 | 0.12 | ≤ 0.4 | 4, 6, 8, 10 | Ø1.000–1.010 | 0.785 |
| 1.5 | h6 | 1.500 | 1.494 | 0.16 | ≤ 0.4 | 6, 8, 10, 12 | Ø1.500–1.513 | 1.767 |
| 2.0 | h6 | 2.000 | 1.994 | 0.20 | ≤ 0.4 | 6, 8, 10, 12, 16 | Ø2.000–2.013 | 3.142 |
| 3.0 | h6 | 3.000 | 2.994 | 0.25 | ≤ 0.4 | 8, 10, 12, 16, 20 | Ø3.000–3.016 | 7.069 |
| 4.0 | h6 | 4.000 | 3.992 | 0.35 | ≤ 0.4 | 10, 12, 16, 20, 24 | Ø4.000–4.018 | 12.566 |
| 5.0 | h6 | 5.000 | 4.992 | 0.40 | ≤ 0.4 | 12, 16, 20, 24, 30 | Ø5.000–5.018 | 19.635 |
| 6.0 | h6 | 6.000 | 5.992 | 0.50 | ≤ 0.4 | 14, 16, 20, 24, 30, 40 | Ø6.000–6.022 | 28.274 |
| 8.0 | h6 | 8.000 | 7.991 | 0.63 | ≤ 0.4 | 16, 20, 24, 30, 40, 50 | Ø8.000–8.022 | 50.265 |
| 10.0 | h6 | 10.000 | 9.991 | 0.80 | ≤ 0.4 | 20, 24, 30, 40, 50, 60 | Ø10.000–10.022 | 78.540 |
| 12.0 | h6 | 12.000 | 11.989 | 1.00 | ≤ 0.4 | 24, 30, 40, 50, 60, 80 | Ø12.000–12.027 | 113.097 |
| 16.0 | h6 | 16.000 | 15.989 | 1.20 | ≤ 0.4 | 30, 40, 50, 60, 80, 100 | Ø16.000–16.027 | 201.062 |
| 20.0 | h6 | 20.000 | 19.987 | 1.60 | ≤ 0.4 | 40, 50, 60, 80, 100, 120 | Ø20.000–20.033 | 314.159 |
| 25.0 | h6 | 25.000 | 24.987 | 2.00 | ≤ 0.4 | 50, 60, 80, 100, 120, 160 | Ø25.000–25.033 | 490.874 |
| 30.0 | h6 | 30.000 | 29.987 | 2.50 | ≤ 0.4 | 60, 80, 100, 120, 160, 200 | Ø30.000–30.033 | 706.858 |
2.2 — ISO 8752 Spring (Roll) Pin Dimensional Table
| Nominal Dia d (mm) | Hole Size (mm) | Wall Thickness (mm) | Standard Lengths L (mm) | Shear Load — Light (kN) | Shear Load — Heavy (kN) | Material |
|---|---|---|---|---|---|---|
| 2.0 | 2.0 +0.06/0 | 0.4 | 6–20 | 0.8 | 1.3 | Spring steel / SS |
| 2.5 | 2.5 +0.06/0 | 0.5 | 8–24 | 1.3 | 2.0 | Spring steel / SS |
| 3.0 | 3.0 +0.07/0 | 0.6 | 8–32 | 1.9 | 3.0 | Spring steel / SS |
| 4.0 | 4.0 +0.07/0 | 0.8 | 10–40 | 3.3 | 5.3 | Spring steel / SS |
| 5.0 | 5.0 +0.10/0 | 1.0 | 12–50 | 5.2 | 8.3 | Spring steel / SS |
| 6.0 | 6.0 +0.10/0 | 1.0 | 14–60 | 7.5 | 12.0 | Spring steel / SS |
| 8.0 | 8.0 +0.10/0 | 1.2 | 20–80 | 14.0 | 21.5 | Spring steel / SS |
| 10.0 | 10.0 +0.13/0 | 1.5 | 24–100 | 22.0 | 34.0 | Spring steel / SS |
| 12.0 | 12.0 +0.13/0 | 2.0 | 30–120 | 31.5 | 49.0 | Spring steel / SS |
2.3 — Fit Class and Tolerance Reference
| Pin Tolerance | Hole Tolerance | Fit Type | Fit Name | Max Interference (µm) | Assembly Force | Primary Application |
|---|---|---|---|---|---|---|
| h6 | H7 | Transition (slight press) | H7/h6 | 0–22 µm (varies with dia) | Light press or hand drive | Standard precision location — most common |
| n6 | H7 | Interference | H7/n6 | 8–33 µm (varies with dia) | Press fit — hydraulic press required | Permanent location; no disassembly planned |
| m6 | H7 | Transition (press) | H7/m6 | 4–25 µm (varies with dia) | Press fit — light press | Semi-permanent location; rare disassembly |
| h8 | H7 | Clearance (slip) | H7/h8 | 0 (always clearance) | Hand push fit | Alignment only; bolt provides retention |
| f7 | H7 | Clearance (loose) | H7/f7 | 0 (loose clearance) | Finger slide | Easy removal location; frequent maintenance |
| ISO 8734 h6 | H7 reamed | Transition | Standard dowel fit | 0–9 µm (Ø6); 0–11 µm (Ø10) | Mallet or light press | Hydraulic manifolds; machinery alignment |
2.4 — Applicable Standards and Compliance Framework
ISO 8734
Cylindrical dowel pins — unhardened steel and austenitic stainless steel, tolerance class h6. The primary ISO standard for hardened and ground precision dowel pins used in hydraulic manifolds, precision machinery, and tooling. Specifies diameter tolerance (h6), surface finish (Ra ≤ 0.4 µm), chamfer geometry, and length series. Material: hardened carbon steel (min 700 HV) or austenitic SS per grade designation on the order.
ISO 8735
Cylindrical dowel pins of unhardened steel — tolerance class h8. For non-precision location and alignment where a slip-fit assembly is required. Same geometry as ISO 8734 but manufactured to looser h8 tolerance — suitable for alignment-only applications where retention is provided by the assembly bolts. Stainless steel A4-70 version per ISO 8735 widely used for marine and offshore equipment assembly.
DIN 6325
Cylindrical pins, hardened and ground — tolerance m6. The traditional German standard for hardened precision dowel pins. DIN 6325 m6 tolerance class produces a tighter interference fit than ISO 8734 h6, making it suitable for semi-permanent location where the pin is rarely removed. Widely specified in German EPC equipment and machinery documentation — dimensionally compatible with ISO 8734 in the diameter and length range.
DIN 7979
Cylindrical pins with internal thread — for extraction from blind holes. Two types: Type D (threaded both ends) and Type C (threaded one end). The internal thread accepts a standard bolt or slide-hammer puller for extraction without damaging the reamed bore. Mandatory for precision assembly with blind holes — including hydraulic manifold sub-plate dowel locations where the pin must be removed for manifold maintenance. Pin body tolerance h6 per ISO 8734.
ISO 8752 / DIN 1481
Spring-type straight pins — coiled (ISO 8752) and slotted (DIN 1481 / ISO 8752). Coiled spring pins (multi-layer) provide higher fatigue resistance and more even stress distribution than single-layer slotted pins. Light duty (ISO 13337) and heavy duty (ISO 8752) series. Used in hinge pins, linkage assemblies, clevis connections, and any application where shock loads and easy disassembly are design requirements. Material: spring steel or SS; hardness 450–580 HV.
ISO 2339 / DIN 1
Taper pins — 1:50 taper. Available in Form A (small end first) and Form B (large end, threaded for nut). Installed in a tapered reamed hole (reamed with a 1:50 taper reamer). Self-locking under shear load — the taper wedging action increases retention under transverse load. Sized by nominal diameter at the small end and total length. Used in shaft-to-hub connections, linkage pivot pins, and any connection requiring secure mechanical locking with field disassembly capability.
ASME B18.8.2
Taper pins, straight pins, and spring pins — inch series. The governing standard for inch-series dowel and taper pins in North American EPC projects, ASME-coded machinery, and US-specification tooling and fixtures. Specifies dimensions, tolerances, and material requirements for #7/0 to #10 inch taper pins, and diameter sizes from 0.062″ through 1.500″ for straight cylindrical dowel pins.
ISO 3506
Mechanical properties of corrosion-resistant stainless steel fasteners. A2-70 (SS 304) and A4-70 / A4-80 (SS 316) grades for stainless dowel pins in marine, offshore, chemical, and food-grade environments. SS 316 (A4) is the standard marine-grade for offshore and coastal precision assembly. Passivation per ASTM A967 is standard on all SS dowel pin supply. Note: SS dowel pins provide corrosion resistance but lower hardness than carbon steel — verify bearing stress in mating aluminium or soft steel components.
2.5 — Hole Preparation Requirements
| Pin Dia (mm) | Pre-Drill Dia (mm) | Reamer Size (H7) | Reaming Speed (rpm) | Reaming Feed (mm/rev) | Hole Depth — Through | Hole Depth — Blind (min) |
|---|---|---|---|---|---|---|
| 3.0 | 2.8 | 3.000 H7 | 600–1000 | 0.05–0.10 | Pin L + 0.5 mm | Pin L + 3 mm |
| 4.0 | 3.8 | 4.000 H7 | 500–800 | 0.08–0.12 | Pin L + 0.5 mm | Pin L + 4 mm |
| 5.0 | 4.8 | 5.000 H7 | 400–700 | 0.10–0.15 | Pin L + 0.5 mm | Pin L + 5 mm |
| 6.0 | 5.8 | 6.000 H7 | 350–600 | 0.12–0.18 | Pin L + 0.5 mm | Pin L + 6 mm |
| 8.0 | 7.8 | 8.000 H7 | 300–500 | 0.15–0.22 | Pin L + 1.0 mm | Pin L + 8 mm |
| 10.0 | 9.8 | 10.000 H7 | 250–400 | 0.18–0.25 | Pin L + 1.0 mm | Pin L + 10 mm |
| 12.0 | 11.8 | 12.000 H7 | 200–350 | 0.20–0.30 | Pin L + 1.5 mm | Pin L + 12 mm |
| 16.0 | 15.8 | 16.000 H7 | 180–300 | 0.25–0.35 | Pin L + 2.0 mm | Pin L + 16 mm |
| 20.0 | 19.7 | 20.000 H7 | 150–250 | 0.30–0.40 | Pin L + 2.0 mm | Pin L + 20 mm |
Surface Finishes &
Manufacturing Process
Dowel pin material must provide both adequate mechanical strength (hardness, shear capacity, wear resistance) and corrosion resistance for the service environment. RR Hydraulic manufactures dowel pins in all standard and high-performance grades — hardened carbon steel, stainless, tool steel, titanium, and non-magnetic alloys — with full EN 10204 3.1 / 3.2 traceability.
3.1 — Material Grade Overview and Properties
| Material | Spec | Surface Hardness | Core Hardness | UTS (MPa) | Temp Range (°C) | Corrosion Resistance | NACE MR0175 | Primary Application |
|---|---|---|---|---|---|---|---|---|
| Case-Hardened CS (ISO 8734) | ISO 8734 / DIN 6325 | 700–900 HV (case) | 350–500 HV (core) | 1200–1600 | −20 to +200 | Low — must coat | No (exceeds 22 HRC) | Standard precision machinery, tooling, hydraulic |
| Through-Hardened Alloy (58–62 HRC) | 100Cr6 / DIN 17230 | 700–800 HV | 700–800 HV | 1900–2200 | −20 to +150 | Low | No | Highest shear capacity; tooling die pins |
| A2-70 (SS 304) | ISO 3506 / ISO 8734 | 230–270 HV | 230–270 HV | 700 | −196 to +300 | Good | Yes | Food, pharma, mild chemical assembly |
| A4-70 (SS 316) | ISO 3506 / ISO 8734 | 230–270 HV | 230–270 HV | 700 | −196 to +300 | Very Good | Yes | Marine, offshore, chemical, NACE service |
| A4-80 (SS 316 SH) | ISO 3506 | 280–320 HV | 280–320 HV | 800 | −196 to +300 | Very Good | Yes | High-load SS offshore alignment pins |
| Tool Steel (HSS / D2) | DIN 1.3343 / D2 | 830–900 HV | 800–900 HV | 2000–2400 | −20 to +300 | Low | No | Maximum wear resistance; die and mould |
| Titanium Gr.5 | ASTM F835 Ti | 350 HV | 350 HV | 900 | −200 to +315 | Excellent | Yes | Lightweight, non-magnetic, corrosive |
| Brass (CuZn37) | ISO 8839 | 110–150 HV | 110–150 HV | 380 | −200 to +120 | Good | Yes | Non-magnetic, non-sparking, decorative |
| Aluminium (Al Mg3) | EN AW-5754 | 70–90 HV | 70–90 HV | 200–280 | −200 to +120 | Good | Yes | Lightweight precision; aerospace |
3.2 — Corrosion Resistance Matrix
| Material | Indoor Precision Assy | Outdoor / Humid | Marine / Offshore | H₂S / Sour* | Chemical Process | Cryogenic | Non-Magnetic |
|---|---|---|---|---|---|---|---|
| Case-hardened CS (oiled) | Good | Fair | Poor | No | Poor | Fair | No |
| CS + Electroless Nickel | Excellent | Good | Fair | No | Fair | Fair | No |
| A2-70 SS 304 | Excellent | Excellent | Good | Fair | Fair | Excellent | Slightly mag. |
| A4-70 SS 316 | Excellent | Excellent | Excellent | Good | Good | Excellent | Slightly mag. |
| A4-80 SS 316 SH | Excellent | Excellent | Excellent | Good | Good | Excellent | Slightly mag. |
| Titanium Gr.5 | Excellent | Excellent | Excellent | Excellent | Excellent | Excellent | Yes |
| Brass CuZn37 | Excellent | Good | Good | Fair | Fair | Excellent | Yes |
| 100Cr6 Tool Steel | Good (oiled) | Poor | Poor | No | Poor | Fair | No |
3.3 — Surface Finish and Coating Options
| Finish | Spec | Ra (µm) | Salt Spray (h) | Effect on Fit Tolerance | Allowed on Precision Pins? | Application |
|---|---|---|---|---|---|---|
| Hard Ground (bare) | ISO 8734 standard | ≤ 0.4 | <24 | None — as ground | Yes — standard | Precision machinery; hydraulic manifolds; tooling |
| Oiled / Light Rust Inhibitor | Storage protection | ≤ 0.4 (no change) | 48–96 | None | Yes | Precision pins; short storage; remove before precision fit |
| Black Oxide | MIL-DTL-13924 | ≤ 0.5 | 24–72 | Negligible (<0.5 µm) | Yes | Indoor precision; decorative; standard engineering |
| Electroless Nickel (ENP) | ASTM B733 | ≤ 0.4 (replicates ground) | 500–1000 | +5–25 µm per side — verify fit | Conditional — specify undersize pin | Hydraulic; corrosive indoor; hardness increase |
| Hard Chrome | AMS 2406 | ≤ 0.2 (polished after plate) | 500+ | +5–25 µm per side — specify undersize | Conditional — precision grind after plate | Wear-resistant precision pins; high-load shear |
| Zinc Electroplate | ASTM B633 / ISO 4042 | ≤ 0.8 | 96–300 | +5–12 µm — will affect H7 fit | Not recommended for precision h6 pins | Non-precision location pins only; enclosures |
| Passivation (SS only) | ASTM A967 | ≤ 0.4 (no change) | 2000+ | None | Yes | All SS dowel pins — standard finish |
| DLC (Diamond-Like Carbon) | Proprietary PVD | ≤ 0.1 | 2000+ | +1–3 µm per side — minimal | Yes — aerospace/precision | Ultra-high wear resistance; aerospace; cleanroom |
3.4 — Manufacturing Process: Hard Ground Precision Dowel (ISO 8734)
3.4.1 — Bar Stock to Finished Pin
- Bar stock selection: Precision cold-drawn carbon steel or alloy steel bar to nominal diameter +0.3 to +0.5 mm oversize — provides adequate stock for grinding to final tolerance without excessive material removal that could introduce surface stress
- Turning to blanks: CNC turning to nominal length + 1 mm (end grinding stock); OD turned to +0.15 mm above nominal diameter; chamfers formed at both ends to DIN 6325 / ISO 8734 specification
- Heat treatment — case hardening: Gas carburising at 900–950°C for surface case hardness 700–900 HV (59–67 HRC); core maintained ductile at 350–500 HV for impact resistance; case depth 0.3–0.8 mm depending on pin diameter
- Centreless grinding: Precision centreless grinding to final h6 tolerance — dimensional accuracy ±3 µm across the grinding batch; Ra ≤ 0.4 µm (surface finish measured by profilometer on sampled units)
- Lapping (optional): Lapping to Ra ≤ 0.2 µm for ultra-precision bearing and alignment pin applications — particularly for DLC-coated pins where the substrate surface finish determines the final coating quality
- End grinding: Both ends ground flat and square within 0.01 mm of pin axis; chamfers maintained at specified angle and length per ISO 8734 chamfer table
- Demagnetisation: Mandatory for pins used in instrument, sensor, or MRI-adjacent assemblies; verified with residual field gauge (max 1 mT)
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from raw bar stock to final packed shipment on all dowel pin orders. Dimensional inspection to micrometre accuracy, hardness certificates, surface finish reports, EN 10204 MTRs, and complete EPC export documentation packages are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | Signatory | Standard EPC Requirement | When Mandatory |
|---|---|---|---|---|
| 2.1 | Conformity declaration only | Manufacturer | Non-critical general assembly | Commercial hardware procurement only |
| 2.2 | Non-specific test results | Manufacturer | Standard EPC machinery / equipment | General EPC precision machinery alignment pins |
| 3.1 | Heat/bar lot traceable mech + chem | Manufacturer’s authorised QC | Hydraulic manifolds, NACE, SS offshore, critical | All hydraulic manifold dowels, NACE, offshore SS |
| 3.2 | 3.1 + countersigned by TPI | Manufacturer + SGS / BV / Lloyds | Critical offshore, nuclear, ATEX | Offshore structural alignment, nuclear Class 1/2 |
4.3 — Applications by Industry
Hydraulic Manifold Sub-Plate Alignment
The most demanding dowel pin application in EPC hydraulic systems. Two ISO 8734 Ø6–Ø8 mm h6 precision pins locate each hydraulic sub-plate or valve body to the manifold block — aligning the fluid ports to within ±0.05 mm to prevent port-to-port leakage across the sealing face. Threaded extraction version (DIN 7979) mandatory for all blind-hole manifold dowels — maintenance requires sub-plate removal without damaging the precision bore. Material: case-hardened carbon steel standard; SS A4-70 for chemical process and offshore hydraulic manifolds.
Pump and Compressor Housing Register
Solid cylindrical dowel pins (ISO 8734, DIN 6325) locate pump casings, compressor cylinder heads, and gear case covers to their respective bodies — ensuring the internal bore registers are co-axial after reassembly within the design clearance tolerance. Two dowels per split line are standard; three for large compressor casings. Precision here directly affects bearing alignment, shaft runout, and seal performance. Carbon steel pins with electroless nickel for corrosive process fluid service.
Equipment Base Frame Alignment
Large-diameter (Ø16–Ø30 mm) precision dowel pins align equipment base frames — pump-motor sets, compressor trains, and gearbox assemblies — to their concrete or steel foundations after initial alignment and grouting. The dowels are installed after final precision shaft alignment to lock the equipment feet to the foundation plate, preserving the alignment condition for life of plant. Material: through-hardened or case-hardened steel; HDG or electroless nickel for outdoor and coastal facilities.
Precision Tooling and Jig Fixtures
ISO 8734 hardened ground dowel pins (100Cr6 or tool steel grade for maximum wear resistance) in precision jigs, fixtures, and assembly tooling. Location repeatability of ±2–5 µm required for welding jigs, inspection fixtures, and high-tolerance assembly aids. Pins replaced on a planned maintenance cycle as wear causes position drift. DLC-coated pins for long-life tooling with minimum maintenance intervals.
Offshore Equipment Assembly
SS A4-70 or A4-80 ISO 8734 precision dowel pins for all offshore precision assembly — pump housing covers, valve body alignment, subsea tree component location, and topside instrument panel indexing. Carbon steel pins are unacceptable in offshore marine atmosphere — corrosion causes pin seizure in the reamed bore within months, preventing disassembly for maintenance. PMI on every SS lot mandatory. All offshore dowel pin supply with EN 10204 3.1 and passivation per ASTM A967.
Food and Pharmaceutical Precision Machinery
SS A4-70 or A4-80 dowel pins with smooth, chamfered ends and Ra ≤ 0.4 µm surface finish in hygienic precision assemblies — filling machine indexing, tablet press die plate location, and homogeniser pump cover alignment. PTFE-coated or passivated SS for chemical CIP (clean-in-place) resistance. No crevices at the pin-hole interface: through-holes preferred over blind holes; thread-free pin body to eliminate bacteria trapping. Full traceability to EN 10204 3.1 per EU 10/2011 / 21 CFR requirements.
4.4 — Export Packaging Specification
- Precision ISO 8734 / DIN 6325 pins individually wrapped in VCI paper or lightly oiled and packed in compartmented polystyrene trays — each pin separated to prevent contact damage to the precision ground surface; surface scratches on h6 pins directly affect fit tolerance
- Lot packaging: individual trays per diameter and length labelled with ISO 8734 or DIN standard reference, nominal diameter, tolerance class, length, material, surface finish, hardness range, heat/lot number, and PO item reference
- SS pins: individually VCI-wrapped and segregated from carbon steel pins — iron contamination on the SS surface causes corrosion spots; segregation maintained through the full packaging and transit chain
- Spring pins and taper pins: packed in polybags per diameter and length — no individual wrapping required but VCI bag for carbon steel grades; lot label per polybag
- Long pins (L > 10× diameter): packed horizontally in padded tubes or channels to prevent bending during transit; any bow exceeding the ISO 8734 straightness tolerance renders the pin scrap
- Critical precision lots (h6 tolerance): dimensional inspection report enclosed with each lot showing individual measurements for the lot sample — not just a conformity certificate
- ISPM-15 heat-treated timber crates for all international export; inner packaging per UN requirements for precision engineered components
- Documentation: packing list, EN 10204 MTC, dimensional inspection report, hardness certificate, surface finish report, and FAI report enclosed with each lot
4.5 — Complete EPC Project Documentation Package
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 2.2 / 3.1 / 3.2 | Mandatory — grade per project spec | Bar stock lot heat-traceable |
| 02 | Chemical Composition Report | Bar stock lot certified lab analysis | Mandatory — 3.1 / 3.2 orders | Per ISO 8734 / DIN 6325 / ISO 3506 |
| 03 | Mechanical Properties Report | UTS, hardness (case + core) | Mandatory — 3.1 / 3.2 orders | Surface + core hardness; case depth |
| 04 | Hardness Test Report | ISO 6507 Vickers | Mandatory — all precision pins | Case HV + core HV + case depth per lot |
| 05 | Dimensional Inspection Report | Per ISO 8734 / DIN 6325 / ASME B18.8.2 | Mandatory | OD, cylindricity, length, chamfer — µm data |
| 06 | Surface Finish (Ra) Report | ISO 4287 / ISO 1302 | Mandatory — precision h6 pins | Ra ≤ 0.4 µm per ISO 8734; profilometer measurement |
| 07 | Straightness Report | V-block + dial gauge per ISO 8734 | Mandatory — h6 precision pins | Max 0.003 mm per 100 mm confirmed |
| 08 | Coated Pin Diameter Report | Micrometer post-coating | Conditional — coated precision pins | Final OD confirms fit tolerance maintained |
| 09 | PMI Report (XRF) | Per lot — SS / Ti / tool steel | Mandatory — non-CS precision pins | A4-70 vs A2-70 differentiation |
| 10 | First Article Inspection (FAI) Report | Project-specific format + full dim. data | Mandatory — new configs / first lots | Released before batch production |
| 11 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — EN 10204 3.2 / offshore | Co-witness dimensional and hardness at works |
| 12 | NACE Compliance Statement | Material + hardness declaration | Conditional — sour service supply | SS only; carbon steel excluded |
| 13 | Demagnetisation Certificate | Residual field ≤ 1 mT | Conditional — sensor / instrument adjacent | Verified by residual field gauss measurement |
| 14 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers precision pin manufacture |
| 15 | Country of Origin Certificate | Chamber of Commerce | Mandatory — all export | HS tariff code for customs classification |
| 16 | Packing List | Item-level per shipment | Mandatory | Cross-references lot numbers and MTC |
| 17 | Commercial Invoice | Per INCOTERMS 2020 | Mandatory | Includes HS tariff code |
| 18 | Bill of Lading / Air Waybill | Per freight mode | Mandatory | Issued by freight forwarder |
4.6 — ISO and Quality System Compliance
ISO 9001:2015
Quality Management System covering bar stock procurement and certification, CNC turning process control, heat treatment Q&T and case hardening process qualification, centreless grinding dimensional control and gauge calibration (micrometer accuracy traceable to national standards), surface finish measurement protocol, straightness inspection, coating process control, and full lot traceability. Mandatory for all EPC, hydraulic, and precision machinery project procurement qualification.
ISO 10474
Steel and steel products — inspection documents. Source framework for EN 10204 certificate types. Some EPC project and precision machinery specifications reference ISO 10474 Type 3.1.B (= EN 10204 3.1) for dowel pin material certification. RR Hydraulic provides documentation in either format and cross-maps for legacy specification compliance, including German EPC specifications referencing DIN standards.
ISO 4413
Safety requirements for hydraulic fluid power systems. Dowel pins are safety-critical components in hydraulic manifold sub-plate assemblies — they maintain port alignment under hydraulic pressure loading and valve actuation forces. ISO 4413 requires that hydraulic manifold connections maintain fluid containment under design pressure with appropriate safety factors; precision dowel pin alignment is a fundamental prerequisite for sub-plate face seal integrity in ISO 4413 compliant hydraulic systems.
VDI 2230
Systematic calculation of highly stressed bolted joints. While VDI 2230 primarily addresses bolted joints, its companion analysis for shear-loaded precision connections covers the combined shear-bolt joint where dowel pins carry the shear component and bolts carry the axial clamping load — the standard configuration in hydraulic manifold and precision machinery sub-plate assembly. The dowel pin shear capacity and bearing stress calculations per VDI 2230 are used in conjunction with the manifold bolt torque analysis for complete joint certification documentation.
Submit your pin type, diameter, tolerance class, length, material, finish, and quantity to RR Hydraulic for a complete, certified commercial offer.