For inch hex-socket shoulder screws, ASME B18.3 fixes the geometry and the tolerances. 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 is "Socket cap, shoulder, set screws, and hex keys (inch series)". An inch-series document.
Material, property class, surface finish and packaging are governed by separate documents — ISO 898-1 and ISO 898-2 for mechanical property classes, ISO 4042 for electroplated finishes.
Tolerance & Product Grades
ASME B18.3 does not divide inch hex-socket shoulder screws into product grades. Tolerances are given as limits on the individual dimensions in the table.
Where a general-tolerance class is cited on the drawing instead, it applies to the dimensions not otherwise toleranced.
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.
Custom manufacturing · Made to drawing
Need a bolt to this standard in a non-standard size?
Parts built to ASME B18 3 are already in the catalog, so a special is usually a variation on existing tooling rather than a new design — which is what keeps the cost down. Made by cold heading or hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
