Threads / Size reference
#6-40 UNF
#6-40 has a nominal outside diameter of 3.5052 mm and a 0.635 mm pitch.
3.5052 mm
0.635 mm pitch
Nominal dimensions; no class allowances or acceptance limits applied. The # prefix denotes a numbered screw, not millimetres.
same diameter comparison
#6-40 vs #6-32
#6-32 UNC shares the nominal diameter but has a 0.793750 mm pitch. The pitch difference is 0.158750 mm; these are different nominal threads.
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Cutting-tap drill references
| Target theoretical thread | Listed drill | Diameter · in / mm |
|---|---|---|
| 55% | #31 | 0.12 / 3.048 |
| 65% | #32 | 0.116 / 2.9464 |
| 75% | #33 | 0.113 / 2.8702 |
Need acceptance limits?
The complete class and applicable drawing requirements are needed. These nominal values are not maximum/minimum inspection limits.
Part has no marking?
Measure the correct diameter and pitch, then compare candidates across metric and inch systems.
Basis for this size
Nominal designation and family transcribed from the live directory on 2026-10-19; unit conversions are calculated using exactly 25.4 mm/in. The drill row was read from Guhring PDF page 2; numbered and letter drill diameters use page 1. Paid standard limit tables have not been reviewed.
ASME B1.1 · standard scope ↗ · Guhring · Tap Drill Sizes ↗ Full source scope →