UNC brass machine screw nut (ASME B18.6.3) — engineering drawing (Brassland).
Specification
| Standard | ASME B18.6.3 (machine screw nuts, hex) |
| Type | Hex machine screw nuts, inch series #0 – 3/8 |
| Thread | UNC and UNF pitches on the same body (e.g. #10-24 / #10-32); to ASME B1.1, internal class 2B |
| Material | C36000 free-machining brass (UNS) — EN twin CW614N (CuZn39Pb3); lead-free C69300 / CW724R on request |
| Certificate | EN 10204 3.1 per shipment; 3.2 on request |
Datasheet — hex machine screw nuts to ASME B18.6.3
| Size | Basic major dia | A/F basic | A/F max | A/F min | Corners max | Corners min | Thickness max | Thickness min |
|---|---|---|---|---|---|---|---|---|
| #0 | 0.0600 | 5/32 (0.156) | 0.156 | 0.150 | 0.221 | 0.206 | 0.050 | 0.043 |
| #1 | 0.0730 | 5/32 | 0.156 | 0.150 | 0.221 | 0.206 | 0.050 | 0.043 |
| #2 | 0.0860 | 3/16 (0.188) | 0.188 | 0.180 | 0.265 | 0.247 | 0.066 | 0.057 |
| #3 | 0.0990 | 3/16 | 0.188 | 0.180 | 0.265 | 0.247 | 0.066 | 0.057 |
| #4 | 0.1120 | 1/4 (0.250) | 0.250 | 0.241 | 0.354 | 0.331 | 0.098 | 0.087 |
| #5 | 0.1250 | 5/16 (0.312) | 0.312 | 0.302 | 0.442 | 0.415 | 0.114 | 0.102 |
| #6 | 0.1380 | 5/16 | 0.312 | 0.302 | 0.442 | 0.415 | 0.114 | 0.102 |
| #8 | 0.1640 | 11/32 (0.344) | 0.344 | 0.332 | 0.486 | 0.456 | 0.130 | 0.117 |
| #10 | 0.1900 | 3/8 (0.375) | 0.375 | 0.362 | 0.530 | 0.497 | 0.130 | 0.117 |
| #12 | 0.2160 | 7/16 (0.438) | 0.438 | 0.423 | 0.619 | 0.581 | 0.161 | 0.148 |
| 1/4 | 0.2500 | 7/16 | 0.438 | 0.423 | 0.619 | 0.581 | 0.193 | 0.178 |
| 5/16 | 0.3125 | 9/16 (0.562) | 0.562 | 0.545 | 0.795 | 0.748 | 0.225 | 0.208 |
| 3/8 | 0.3750 | 5/8 (0.625) | 0.625 | 0.607 | 0.884 | 0.833 | 0.257 | 0.239 |
Dimensions in inches to ASME/ANSI B18.6.3. #10-24 and #10-32 share the same #10 nut body. Commercial “small pattern” hex nuts run a smaller across-flats than this table — those follow the supplier datasheet, not B18.6.3. Full dimension chart: ASME B18.6.3 machine screw nut dimension chart →
B18.6.3 vs B18.2.2 — don’t mix the tables
Where the two ranges overlap (1/4, 5/16 and 3/8 in.), B18.6.3 machine screw nuts are thinner than B18.2.2 finished hex nuts, and the across-flats also differ at some sizes (a 5/16 machine screw nut is 9/16 in. A/F where the B18.2.2 hex nut is 1/2 in.). The two series are not interchangeable — pick the standard your assembly calls out. For 1/4–3/4 in. full nuts and jam nuts, see UNC hex & jam nuts (ASME B18.2.2).
Applications
Machine screw nuts pair with #0–3/8 machine screws in electronics and PCB hardware, instrument assemblies, terminal and switchgear hardware, and small appliance and panel fixings. Brass versions add corrosion resistance, conductivity and a clean cosmetic finish; tin or nickel plating is available. All production is made to order with sizes, threads and packaging to your specification.
Imperial & UNC range
Related pages
1/4–3/4 in. nuts to ASME B18.2.2.
View →ProductAll DIN / ISO / ANSI nut types.
View →MetricMetric thin-pattern hex nuts.
View →MaterialUS free-machining brass datasheet.
View →IndustrySmall brass hardware for boards.
View →ToolUNC / UNF / metric side by side.
View →Quote in 24 hours.
Give the standard, thread, finish and quantity. We machine inch-series brass parts in Jamnagar, India, and export to 40+ countries.
Sources & references
Dimension table per ASME/ANSI B18.6.3, cross-checked cell-for-cell against two concordant published references, including the Engineers Edge hexagon machine screw nut table (verified July 2026). Governing document: ASME B18.6.3.
Frequently asked questions
ASME B18.6.3 (machine screw nuts) — not ASME B18.2.2, which starts at 1/4 in. A #4-40 machine screw nut has a 1/4 in. width across flats and a 0.098 in. maximum thickness.
Yes. At the overlapping 1/4, 5/16 and 3/8 in. sizes, B18.6.3 machine screw nuts are thinner than B18.2.2 finished hex nuts, and the across-flats also differ at some sizes — a 5/16 machine screw nut is 9/16 in. A/F versus 1/2 in. for the B18.2.2 hex nut. The two tables must not be mixed.
No. Both pitches use the same #10 nut body — 3/8 in. across flats, 0.130 in. maximum thickness. Only the internal thread differs.
A commercial variant with a smaller width across flats than the B18.6.3 table. Small-pattern dimensions follow the individual supplier datasheet rather than the standard — if your drawing calls one out, we machine to the drawing.
C36000 free-machining brass, the EN twin of CW614N (CuZn39Pb3). Tin or nickel plating and lead-free alloys (C69300 silicon brass) are available on request.