For jam nuts (thin hex, inch), ASME B18.2.2 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 B18.2.2 — 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 jam nuts (thin hex, inch) 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
| Thread size | Across flats s (mm) | Across corners e (mm) | Nut height m (mm) | Across flats (in) | Nut height (in) | Reference standard |
|---|---|---|---|---|---|---|
| 1/4"-20 | 11.11 | 12.70 | 3.97 | 7/16 | 5/32 | ASME B18.2.2 |
| 5/16"-18 | 12.70 | 14.53 | 4.76 | 1/2 | 3/16 | ASME B18.2.2 |
| 3/8"-16 | 14.29 | 16.35 | 5.56 | 9/16 | 7/32 | ASME B18.2.2 |
| 7/16"-14 | 17.46 | 19.98 | 6.35 | 11/16 | 1/4 | ASME B18.2.2 |
| 1/2"-13 | 19.05 | 21.79 | 7.94 | 3/4 | 5/16 | ASME B18.2.2 |
| 9/16"-12 | 20.64 | 23.62 | 7.94 | 13/16 | 5/16 | ASME B18.2.2 |
| 5/8"-11 | 23.81 | 27.23 | 9.53 | 15/16 | 3/8 | ASME B18.2.2 |
| 3/4"-10 | 28.58 | 32.69 | 11.11 | 1-1/8 | 7/16 | ASME B18.2.2 |
| 7/8"-9 | 33.34 | 38.14 | 12.70 | 1-5/16 | 1/2 | ASME B18.2.2 |
| 1"-8 | 38.10 | 43.59 | 14.29 | 1-1/2 | 9/16 | ASME B18.2.2 |
| 1-1/8"-7 | 42.86 | 49.04 | 15.88 | 1-11/16 | 5/8 | ASME B18.2.2 |
| 1-1/4"-7 | 47.63 | 54.48 | 17.46 | 1-7/8 | 11/16 | ASME B18.2.2 |
Companion Standards
ASME B18.2.2 controls only the geometry of jam nuts (thin hex, inch). The mechanical strength is set by ISO 898-1 (bolts, screws and studs) or ISO 898-2 (nuts); the surface finish is governed by separate finish standards such as ISO 4042 for electroplating. For corrosion testing, the relevant document is ISO 9227 (neutral salt spray).
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.
