#0-80 UNF Tap Drill Size
The number you came for, then the reasoning behind it.
#0-80 UNF tap drill — 75% thread
3/64
0.0469" · 1.2 mm metric equivalent
How it's calculated
Tap drill = major diameter − (0.01299 × %thread) / TPI → 0.0600 − (0.01299 × 75) / 80 = 0.0478"
The nearest standard drill above that is 3/64 at 0.0469".
All engagement percentages
| % thread | Exact hole | Inch drill | Metric equivalent |
|---|---|---|---|
| 50% | 0.0519" | #55 (0.0520") | 1.3 mm |
| 65% | 0.0494" | #55 (0.0520") | 1.3 mm |
| 75% | 0.0478" | 3/64 (0.0469") | 1.2 mm |
| 85% | 0.0462" | #56 (0.0465") | 1.2 mm |
Which percentage should you actually use?
75% for through-holes in mild steel and aluminium. 65% for blind holes, stainless, titanium and anything where the tap is at risk. 50% for hand-tapping deep holes. The strength you give up going from 75% to 60% is around 5%; the tapping torque you give up is around 30%. In practice the threads almost never fail — the tap does.
75% for through-holes in mild steel and aluminium. 65% for blind holes, stainless, titanium and anything where the tap is at risk. 50% for hand-tapping deep holes. The strength you give up going from 75% to 60% is around 5%; the tapping torque you give up is around 30%. In practice the threads almost never fail — the tap does.