ASME B18.2.2 Hex Nut — Inch Series
The inch-series finished hex nut in UNC. Height and width across flats are held to inch dimensions, so it will not match a metric wrench even where the thread diameter is close.
Where it is used
The finished hex nut in inch series is the standard mating nut for B18.2.1 hex cap screws and inch studs. It appears wherever a bolted joint is assembled on site rather than in a controlled shop, because it can be run down with an ordinary inch wrench and does not need a tapped hole.
How to choose it
Match the nut grade to the bolt: an SAE Grade 8 bolt needs a Grade 8 nut, otherwise the thread strips first and the joint fails at the nut instead of the bolt. The standard finished nut is the same width across flats as the matching bolt head so one wrench serves both. Heavy hex nuts are a separate product and are taller and wider; they are called out on structural drawings, not interchangeable with finished nuts.
Dimensions8 sizes · inches
| Thread | TPI | Width across flats s (in) | Nut height m (in) | Width across corners (in) |
|---|---|---|---|---|
| 1/4-20 | 20 | 0.4375 | 0.2188 | 0.505 |
| 5/16-18 | 18 | 0.5 | 0.2656 | 0.577 |
| 3/8-16 | 16 | 0.5625 | 0.3281 | 0.65 |
| 1/2-13 | 13 | 0.75 | 0.4219 | 0.866 |
| 5/8-11 | 11 | 0.9375 | 0.5313 | 1.083 |
| 3/4-10 | 10 | 1.125 | 0.6406 | 1.299 |
| 7/8-9 | 9 | 1.3125 | 0.75 | 1.516 |
| 1-8 | 8 | 1.5 | 0.8438 | 1.732 |
Nominal dimensions in inches as published in ASME B18.2.2. Tolerances, material requirements and marking are defined separately by the issuing body.
Available sizeslinked to individual specification pages
Thread referencesused by the sizes above
Fitting and interchange notes
Width across flats is inch-dimensioned, so a 1/4-20 nut takes a 7/16 in wrench — the metric M6 nut takes a 10 mm. Threads are UNC by default with UNF available. Note that inch nuts are dimensioned across flats while some metric standards specify across corners, so the two figures should not be compared directly when checking a drawing.