Verified by Rachel Mayfield, Supply Chain Analyst - August 2026
A #8-32 machine screw has a 0.164" (4.17 mm) major diameter and 32 threads per inch. The tap drill for a standard 75% thread is #29 (0.136"), the normal-fit clearance drill is #16 (0.177"), a pan head measures 0.322" across, and the matching machine screw nut takes a 11/32" wrench. The fine-thread version is #8-36 UNF.
#8-32 thread, tap drill and torque
| Property | #8-32 (UNC) | #8-36 (UNF) | Reference |
|---|
| Nominal major diameter | 0.164" (4.17 mm) | 0.164" (4.17 mm) | ASME B1.1 |
| Threads per inch | 32 TPI | 36 TPI | ASME B1.1 |
| Thread pitch | 0.79 mm | 0.71 mm | 1 / TPI |
| Tap drill (75% engagement) | #29 (0.136") | #29 (0.136") | Standard tap drill chart |
| Tensile stress area | 0.014 in² | 0.01474 in² | ASME B1.1 |
| Typical torque, 18-8 stainless, dry | 19.8 in-lb | 22.0 in-lb | Published torque charts |
The number-size diameter comes from the ASME B1.1 formula 0.060" + 0.013" x screw number, so #8 is 0.060 + 0.104 = 0.164". Torque values are typical dry figures for 18-8 stainless or low-carbon steel screws from the common published charts, in inch-pounds; a screwdriver-driven fastener this size is normally tightened by feel and these numbers are a ceiling, not a target.
#8-32 clearance hole sizes
| Fit | Drill | Diameter | Reference |
|---|
| Close | #18 | 0.170" | ASME B18.2.8 |
| Normal | #16 | 0.177" | ASME B18.2.8 |
| Loose | #13 | 0.185" | ASME B18.2.8 |
Use the normal fit for general assembly. Close fit is for located parts where the screw is doing alignment duty; loose fit is for painted or plated parts, stacked tolerances and anything that has to go together in the field.
#8-32 screw head dimensions by head type
| Head type | Head diameter (max) | Head height | Drive | Reference |
|---|
| Pan head (slotted or Phillips) | 0.322" | 0.096" | Phillips #2 | ASME B18.6.3 |
| Flat countersunk head, 82° | 0.332" | 0.100" | Phillips #2 | ASME B18.6.3 |
| Socket head cap screw | 0.270" | 0.164" | hex key 9/64" | ASME B18.3 |
| Button head socket screw | 0.312" | 0.092" | hex key 3/32" | ASME B18.3 |
Head diameters are maximums from the standard. Slotted and Phillips pan heads share the same envelope. The 82-degree flat head is the US standard; the 90-degree countersink used on metric screws to ISO 7046 will not seat an 82-degree head properly, which matters when imperial screws go into metric-drilled parts.
Where #8 screws are used
Typical applications: switch plates, hinges, terminal strips, machine guards and general sheet-metal assembly. The machine screw nut for this size is 11/32" across flats (ASME B18.6.3).
Metric near-equivalent
The nearest metric size to #8 is M4 (4.17 mm against 4.0 mm). Near is not equal: a #8-32 will not run in a metric tapped hole and a metric screw will strip a #8 thread. For metric cards see MLC's M3, M4 and M5 screw dimension pages.
Other number sizes
#4-40, #6-32, #10-24, #12-24. Larger sizes move to fractional bolts: 1/4-20 and up. Full thread tables on the UNC/UNF thread chart and the tap drill and clearance hole chart.
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