Verified by Rachel Mayfield, Supply Chain Analyst - August 2026
A #6-32 machine screw has a 0.138" (3.51 mm) major diameter and 32 threads per inch. The tap drill for a standard 75% thread is #36 (0.106"), the normal-fit clearance drill is #25 (0.149"), a pan head measures 0.270" across, and the matching machine screw nut takes a 5/16" wrench. The fine-thread version is #6-40 UNF.
#6-32 thread, tap drill and torque
| Property | #6-32 (UNC) | #6-40 (UNF) | Reference |
|---|
| Nominal major diameter | 0.138" (3.51 mm) | 0.138" (3.51 mm) | ASME B1.1 |
| Threads per inch | 32 TPI | 40 TPI | ASME B1.1 |
| Thread pitch | 0.79 mm | 0.64 mm | 1 / TPI |
| Tap drill (75% engagement) | #36 (0.106") | #33 (0.113") | Standard tap drill chart |
| Tensile stress area | 0.00909 in² | 0.01015 in² | ASME B1.1 |
| Typical torque, 18-8 stainless, dry | 9.6 in-lb | 12.1 in-lb | Published torque charts |
The number-size diameter comes from the ASME B1.1 formula 0.060" + 0.013" x screw number, so #6 is 0.060 + 0.078 = 0.138". 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.
#6-32 clearance hole sizes
| Fit | Drill | Diameter | Reference |
|---|
| Close | #27 | 0.144" | ASME B18.2.8 |
| Normal | #25 | 0.149" | ASME B18.2.8 |
| Loose | #18 | 0.170" | 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.
#6-32 screw head dimensions by head type
| Head type | Head diameter (max) | Head height | Drive | Reference |
|---|
| Pan head (slotted or Phillips) | 0.270" | 0.082" | Phillips #2 | ASME B18.6.3 |
| Flat countersunk head, 82° | 0.279" | 0.083" | Phillips #2 | ASME B18.6.3 |
| Socket head cap screw | 0.226" | 0.138" | hex key 7/64" | ASME B18.3 |
| Button head socket screw | 0.262" | 0.077" | hex key 5/64" | 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 #6 screws are used
Typical applications: electrical boxes and cover plates, computer cases, appliance panels and light brackets. The machine screw nut for this size is 5/16" across flats (ASME B18.6.3).
Metric near-equivalent
The nearest metric size to #6 is M3.5 (3.51 mm against 3.5 mm). Near is not equal: a #6-32 will not run in a metric tapped hole and a metric screw will strip a #6 thread. For metric cards see MLC's M3, M4 and M5 screw dimension pages.
Other number sizes
#4-40, #8-32, #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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