Shoulder Bolts

Precision Socket Shoulder Screws for Pivot, Guide, Spacer & Locating Applications

Shoulder Bolts, also known as Socket Shoulder Screws or Stripper Bolts, combine a cylindrical Hex Socket Head, precision unthreaded shoulder and smaller-diameter threaded end. The smooth shoulder acts as a functional pivot, guide, spacer, bearing surface or locating feature while the reduced thread retains the fastener.

Structure

Hex Socket Head + Precision Shoulder + Reduced Thread

Technical Reference

ISO 7379:1983

Shoulder Range

Ø6.5–25 mm

Thread Range

M5–M20

Shoulder Tolerance

f9 for ISO 7379

Primary Drive

Internal Hex Socket

Materials

304 / A2, 316 / A4 Stainless Steel and Alloy Steel

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Product Overview

The precision shoulder is not simply an unthreaded bolt shank. It is a controlled cylindrical functional surface used for pivoting, sliding, guiding, spacing and locating in machinery, tooling and automation assemblies.

Shoulder diameter is intentionally larger than thread diameter. The physical step establishes the shoulder seating surface, while the smaller threaded end provides retention in a tapped component. Correct selection keeps the moving or guided component on the smooth shoulder rather than directly on the screw thread.

Buyers should specify standard or custom configuration, shoulder diameter and length, thread size, pitch and length, head and socket geometry, material, shoulder tolerance, surface finish or roughness, hardness, quantity and any drawing or sample requirements.

Technical Specifications

Product / Alternative Names

Shoulder Bolts / Socket Shoulder Screws / Stripper Bolts

Primary Technical Standard

ISO 7379:1983, Hexagon socket head shoulder screws; current and reconfirmed by ISO in 2025

Head / Drive

Cylindrical Socket Head; Internal Hex / Hex Socket

Shoulder

Precision unthreaded cylindrical shoulder; standard ISO tolerance f9

ISO Shoulder / Thread Pairs

Ø6.5→M5; Ø8→M6; Ø10→M8; Ø13→M10; Ø16→M12; Ø20→M16; Ø25→M20

Metric Coarse Pitch

M5×0.8; M6×1.0; M8×1.25; M10×1.5; M12×1.75; M16×2.0; M20×2.5

Materials

304/A2, 316/A4 Stainless Steel, Alloy Steel and Carbon Steel where applicable; property class 12.9 available according to requirement

Typical Functions

Pivot, guide, spacer, stop, bearing surface and locating element

Key Dimensions

ds, ls, d, P, b, dk, k, socket s/depth t, transition radius and thread relief

Shoulder Diameter, Shoulder Length & Precision Fit Selection

Three Functional Zones

Cylindrical hex socket head → large smooth precision shoulder → smaller machine-threaded end.

Shoulder Diameter ds

Controls pivot diameter, guide fit, bore interface and locating accuracy. It must not be confused with thread diameter d.

f9 Shoulder Tolerance

ISO 7379 applies an f9 zone whose actual limits vary by nominal shoulder diameter; one fixed tolerance must not be used for every size.

Shoulder Length ls

Measured from under the head to the shoulder step, not to the threaded tip. It controls pivot width, spacer distance, stack and guide position.

Reduced Thread

The thread is intentionally smaller than the shoulder; for example, strict ISO 7379 pairs a Ø10 shoulder with an M8 thread.

Shoulder Seating

Hole depth must allow the thread to engage and the shoulder step to seat before the threaded end bottoms out.

Mating Bore

Fit depends on shoulder tolerance, bore tolerance, clearance, motion, lubrication, temperature and alignment. H7 is not universally mandatory.

Surface / Load Path

Finish influences pivot, slide, bearing and guide behavior. Actual capacity depends on diameter, material, heat treatment, loading and support geometry.

Stainless Steel, Alloy Steel & Size Options

1304 / A2 Stainless Steel — Primary corrosion-resistant option for machinery, fixtures and equipment; lubrication and material pairing should be considered for moving surfaces.

2316 / A4 Stainless Steel — Increased corrosion resistance for outdoor, coastal, humid and process environments.

3Alloy Steel — Important for tooling, machinery, wear and higher mechanical loads; property class 12.9 available where applicable.

4ISO & Custom Sizes — ISO shoulders Ø6.5–25 with M5–M20 paired threads; smaller shoulders, inch sizes and special lengths supplied only as custom drawing-based products.

Precision Shoulder & OEM Manufacturing

Shoulder & Thread Variables

Shoulder diameter, length, tolerance, finish, hardness and concentricity; thread diameter, pitch, length, metric coarse/fine or custom UNC/UNF.

Head & Transition

Head diameter/height, hex socket and optional plain or knurled side. Radius, relief, runout and step geometry are controlled for seating and stress transition.

Custom Precision / RFQ

Ground shoulders, tighter drawing tolerances, special finish, material or heat treatment are subject to feasibility review. Send all functional dimensions, surface requirements, quantity and drawing/sample.

Packaging

Protective bags, boxes, export cartons, pallets, precision-surface protection, customer labels, part numbers and authorized private label.

Shoulder, Thread & Dimensional Quality

✓

Shoulder ds & ls

✓

Roundness & Concentricity

✓

Surface Finish

✓

Thread & Hex Socket

✓

Step Radius / Relief

Inspection may cover shoulder diameter and length, f9 or customer tolerance, roundness, cylindricity, concentricity, surface roughness, thread profile and GO/NO-GO fit, socket geometry, step seating, burrs, material and hardness. Order documentation may include MTC, raw-material, dimensional, tolerance, roughness, hardness and thread reports plus third-party support.

Applications

Precision shoulder functions for controlled motion, guidance, spacing and location.

Precision shoulder bolt used as pivot in industrial machinery linkage

Pivoting Linkages

The shoulder acts as a fixed pivot shaft while the threaded end retains the fastener in the stationary component.

Dies, Molds & Stripper Plates

Shoulder Screws or Stripper Bolts guide and limit movement of tooling plates and fixtures.

Rollers, Pulleys & Bearings

The smooth precision shoulder supports compatible rollers, bushings, pulleys or bearing components.

Jigs, Fixtures & Automation

Controlled shoulders provide repeatable guidance, spacing and locating in industrial tooling.

OEM Mechanical Assemblies

Standard ISO 7379 and custom products can be specified by diameter, length, tolerance, material, thread and surface requirement.

Frequently Asked Questions

What is a Shoulder Bolt?

A Shoulder Bolt has a head, a precision unthreaded cylindrical shoulder and a smaller-diameter threaded end. The shoulder can function as a pivot, guide, spacer, bearing surface or locating feature while the thread retains the fastener.

What is the difference between a Shoulder Bolt and a normal Socket Head Cap Screw?

A normal Socket Head Cap Screw is primarily a clamping fastener. A Shoulder Bolt includes a precision larger-diameter smooth shoulder and reduced thread for pivoting, guiding, spacing and locating functions.

What standard applies to Socket Shoulder Screws?

ISO 7379 is the principal international standard for metric Hexagon Socket Head Shoulder Screws. ISO 7379:1983 remains current after reconfirmation in 2025 and covers nominal shoulder diameters from 6.5 through 25 mm.

What does f9 mean on an ISO 7379 Shoulder Screw?

f9 is the dimensional tolerance zone applied to the precision shoulder diameter. Allowable variation depends on nominal shoulder size, so the corresponding ISO limits and mating-bore requirement must be selected together.

What information is required when ordering custom Shoulder Bolts?

Specify shoulder diameter and length, thread size, pitch and length, material, shoulder tolerance, surface finish or hardness, head and drive geometry, quantity and any drawing or sample.