ASME B18.3 specifies the dimensions and tolerances for inch hex-socket shoulder screws. The full dimensional table is reproduced below, followed by the DIN, ISO and ASME parts that match or supersede it.
- Standard
- ASME B18.3
- Product
- Inch Hex-Socket Shoulder Screws
- Governing standards
- ASME B18.3
Equivalence between national standards is dimensional, not always metallurgical. Check the property class separately when substituting.
For inch hex-socket shoulder screws, ASME B18.3 defines the dimensions, tolerances and product grades. The sections below describe the scope of the document, the properties it deliberately leaves to companion standards, and the equivalent designations across standards bodies.
ASME B18.3 — Scope
ASME B18.3 specifies the dimensions and tolerances of inch hex-socket shoulder screws. Material, property class, surface finish and packaging are governed by separate documents in the same standards family (for example ISO 898-1 for the mechanical property classes of bolts and screws).
Tolerance & Product Grades
ASME B18.3, alongside the related ASME B18.3 entries on this site, specifies product grades (typically A or B for fine work and C for general engineering) and tolerance classes for the controlling dimensions. Choose the grade against the precision your application requires.
Dimensions Specified by ASME B18.3
| Shoulder diameter (in) | Shoulder length (in) | Hex socket across-flats (in) | Thread series | Material options | Reference standard |
|---|
| 1/8 | 1/8~1-1/2 | 5/64~1/4 | #4-40 through #10-32 | alloy steel / 303-316 stainless / 416 stainless / brass | ASME B18.3 |
| 1/4 | 1/8~1-1/2 | 5/64~1/4 | #4-40 through 1/4-20 | alloy steel / 303-316 stainless / 416 stainless / brass | ASME B18.3 |
| 1/2 | 1/8~1-1/2 | 5/64~1/4 | #4-40 through 3/8-16 | alloy steel / 303-316 stainless / 416 stainless / brass | ASME B18.3 |
| 3/4 | 1/8~1-1/2 | 5/64~1/4 | 1/4-20 through 1/2-13 | alloy steel / 303-316 stainless / 416 stainless / brass | ASME B18.3 |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Inch Hex-Socket Shoulder Screws page. Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
When to Specify ASME B18.3
ASME B18.3 is the inch-based reference; for metric programs choose the ISO equivalent instead.
Applications & Industries
The sectors that buy Inch Hex-Socket Shoulder Screws to ASME B18.3, and the duty each one buys them for. Stocked from 1/8 to 3/4 (screw size).
Industries that specify Inch Hex-Socket Shoulder Screws
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Die and mold tooling
Guide points where the cylindrical shoulder must be held to size.
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Test fixtures
Replaceable stops and locating posts inside compact assemblies.
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Machine guards
Recessed shoulder hardware where a socket driver clears the surrounding plate.
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Robotic linkages
Socket-head shoulder screws used as repeatable pivots.
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Automotive & transport
Chassis, driveline and body fixings that see vibration and are assembled to a controlled preload.
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Steel fabrication
Bolted connections in frames, enclosures, walkways and weldments, on the bench and on site.
Typical applications
- placing the head in a counterbore while the shoulder carries the part
- specifying shoulder length, diameter and mating thread independently
- using a positive socket drive where a slot would cam out
- providing a controlled shoulder bearing surface with a hex socket head
- bolting brackets, motors and gearboxes to a frame
- assemblies that are dismantled for service and re-torqued
Service conditions to specify against
- Marine and coastal
- Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
- High load
- Supplied in ISO 898-1 property classes, so the joint can be designed to a stated proof load and tightened to a calculated torque rather than by feel.
- Torque and preload
- The joint is designed around bolt tension, so lubrication, coating and the friction coefficient all change the torque figure — state them together.
Where to use something else
- Do not let the mating load run on the thread or socket head; the shoulder is the intended bearing feature.
- Do not use a machine thread into unthreaded sheet or timber; use a tapping screw, rivet nut or insert made for that parent material.
Full application guide: where Inch Hex-Socket Shoulder Screws are used, how to specify them, and the cases they are wrong for
