ASME B18.2.2 Hex Nut Dimensions Chart — UNC/UNF Brass

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ASME B18.2.2 hex nut dimensions — 1/4 to 3/4 in.

ASME B18.2.2, Nuts for General Applications, specifies the dimensions of inch-series finished hex nuts and hex jam nuts from 1/4 in. nominal size upward: width across flats (F), width across corners (G) and thickness (H; H1 for jam nuts), each with basic, max and min values. Thread pitch does not change the nut body — UNC and UNF nuts of the same nominal size are dimensionally identical.

ASME B18.2.2 hex nut and jam nut dimensions — width across flats F, across corners G, thickness H and jam thickness H1

Dimension letters F, G, H and H1 as used in the charts below.

Finished hex nuts — F, G and H

Nominal size	Width A/F F basic	F max	F min	Corners G max	G min	Thickness H basic	H max	H min
1/4	7/16 (0.4375)	0.438	0.428	0.505	0.488	7/32 (0.219)	0.226	0.212
5/16	1/2 (0.500)	0.500	0.489	0.577	0.557	17/64 (0.266)	0.273	0.258
3/8	9/16 (0.5625)	0.562	0.551	0.650	0.628	21/64 (0.328)	0.337	0.320
7/16	11/16 (0.6875)	0.688	0.675	0.794	0.768	3/8 (0.375)	0.385	0.365
1/2	3/4 (0.750)	0.750	0.736	0.866	0.840	7/16 (0.438)	0.448	0.427
5/8	15/16 (0.9375)	0.938	0.922	1.083	1.051	35/64 (0.547)	0.559	0.535
3/4	1-1/8 (1.125)	1.125	1.088	1.299	1.240	41/64 (0.641)	0.665	0.617

Hex jam nuts — thickness H1

Nominal size	Jam thickness H1 basic	H1 max	H1 min
1/4	5/32 (0.156)	0.163	0.150
5/16	3/16 (0.188)	0.195	0.180
3/8	7/32 (0.219)	0.227	0.210
7/16	1/4 (0.250)	0.260	0.240
1/2	5/16 (0.312)	0.323	0.302
5/8	3/8 (0.375)	0.387	0.363
3/4	27/64 (0.422)	0.446	0.398

Dimensions in inches to ASME B18.2.2 (finished hex nuts and hex jam nuts). Jam nuts use the same width across flats F and across corners G as the hex nuts above — only the thickness differs. Threads 1/4-20 to 3/4-10 UNC; UNF pitches (e.g. 1/4-28, 5/16-24, 3/8-24, 1/2-20) run on the same nut body. Sizes above 3/4 in. are machined to drawing.

Governing document: ASME B18.2.2. Values cross-checked against three concordant published references, including the Engineers Edge ANSI/ASME B18.2.2 hex and jam nut tables (verified July 2026).

Scope — where B18.2.2 stops and B18.6.3 begins

ASME B18.2.2 hex nuts start at 1/4 in. nominal size. Smaller inch hex nuts — #4-40, #6-32, #8-32, #10-24 and #10-32 — are machine screw nuts dimensioned to ASME B18.6.3, a separate and slightly thinner series with its own table: see the ASME B18.6.3 machine screw nut chart. Where the two ranges overlap (1/4, 5/16, 3/8 in.), the tables differ and must not be mixed. The metric counterpart of the finished hex nut is the DIN 934 / ISO 4032 pattern.

Need these nuts in brass?

Product

UNC/UNF Brass Hex & Jam Nuts

Machined to ASME B18.2.2 in C36000 free-machining brass — EN 10204 3.1 per shipment.

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Imperial & ANSI Brass Parts

The full UNC/UNF/NPT range — nuts, set screws, standoffs, inserts and flare nuts.

View → Metric equivalent

DIN 934 Brass Hex Nut

The metric twin — ISO 4032 hex nut, M2–M24.

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More reference charts & tools

Chart

ASME B18.6.3 Machine Screw Nuts

#0–3/8 small hex nut dimensions — the series below 1/4 in.

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Thread Size Chart

UNC/UNF, metric, BSP and NPT thread dimensions side by side.

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Tap Drill Chart

Tap-drill sizes for metric, UNC, BSP (G) and NPT threads.

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Frequently asked questions

What does ASME B18.2.2 specify?

ASME B18.2.2, Nuts for General Applications (inch series), specifies the dimensions of several inch nut families including finished hex nuts and hex jam nuts: width across flats (F), width across corners (G) and thickness (H for hex nuts, H1 for jam nuts), each with basic, maximum and minimum values. Hex nuts in the standard start at 1/4 in. nominal size.

Does ASME B18.2.2 cover small sizes like #4-40 or #10-24?

No. ASME B18.2.2 hex nuts start at 1/4 in. nominal size. Smaller inch hex nuts — #4-40, #6-32, #8-32, #10-24 and #10-32 — are machine screw nuts dimensioned to ASME B18.6.3, a separate and slightly thinner series.

What wrench fits a 1/2-13 hex nut?

A 3/4 in. wrench — ASME B18.2.2 gives the 1/2 in. hex nut a basic width across flats of 3/4 in. (0.750 in.). The 1/2 in. jam nut uses the same across-flats with a thinner 5/16 in. body.

Do UNC and UNF hex nuts have different dimensions?

No. Thread pitch does not change the nut body: a 1/4-20 (UNC) and a 1/4-28 (UNF) hex nut share identical width across flats and thickness, and the same holds for the 5/16, 3/8 and 1/2 in. coarse/fine pairs. Only the internal thread differs.

How thick is a jam nut compared with a full hex nut?

Jam nuts keep the same width across flats and across corners but run a thinner body: at 1/2 in. the finished hex nut is 7/16 in. (0.438 in.) thick while the jam nut is 5/16 in. (0.312 in.). Jam nuts are tightened against a full nut as a locking nut, or used where axial space is tight.

Last reviewed: July 2026. This chart is a reference summary — verify against the governing standard and your drawing for procurement-critical work.

ASME B18.2.2 Hex Nut Dimensions