ASME B18.2.2 is the governing dimensional standard for hex flange nuts, unc. This page sets out the scope of the standard, reproduces the full size table it specifies, and lists the DIN/ISO/ASME cross-references commonly cited in datasheets and drawings.
ASME B18.2.2 — Scope
ASME B18.2.2 is "Nuts for general applications: machine screw nuts, hex, square, hex flange, and coupling nuts (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 B18.2.2 does not divide hex flange nuts, unc 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 B18.2.2
| Size | Threads per inch | Width across flats s (in) | B (in) | Nut height m (in) | J (in) | K (in) | Reference standard |
|---|---|---|---|---|---|---|---|
| #6 | 32 | 0.307 | 0.414 | 0.164 | 0.1 | 0.02 | ASME B18.2.2 |
| #8 | 32 | 0.339 | 0.461 | 0.195 | 0.13 | 0.02 | ASME B18.2.2 |
| #10 | 24 | 0.37 | 0.49 | 0.211 | 0.13 | 0.03 | ASME B18.2.2 |
| #12 | 24 | 0.433 | 0.584 | 0.229 | 0.14 | 0.04 | ASME B18.2.2 |
| 1/4" | 20 | 0.433 | 0.584 | 0.229 | 0.14 | 0.04 | ASME B18.2.2 |
| 5/16" | 18 | 0.494 | 0.67 | 0.276 | 0.17 | 0.04 | ASME B18.2.2 |
| 3/8" | 16 | 0.556 | 0.739 | 0.339 | 0.23 | 0.04 | ASME B18.2.2 |
| 7/16" | 14 | 0.681 | 0.923 | 0.385 | 0.26 | 0.04 | ASME B18.2.2 |
| 1/2" | 13 | 0.743 | 1.016 | 0.448 | 0.31 | 0.05 | ASME B18.2.2 |
| 9/16" | 12 | 0.868 | 1.171 | 0.494 | 0.35 | 0.05 | ASME B18.2.2 |
| 5/8" | 11 | 0.93 | 1.264 | 0.557 | 0.4 | 0.05 | ASME B18.2.2 |
| 3/4" | 10 | 1.107 | 1.48 | 0.651 | 0.46 | 0.06 | ASME B18.2.2 |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Hex Flange Nuts, UNC page.
Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
When to Specify ASME B18.2.2
ASME B18.2.2 is the inch-based reference; for metric programs choose the ISO equivalent instead.
Custom manufacturing · Made to drawing
Need a nut to this standard in a non-standard size?
Parts built to ASME B18 2 2 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 tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
