#5-44 UNF Tap Drill Size
The number you came for, then the reasoning behind it.
#5-44 UNF tap drill — 75% thread
#37
0.1040" · 2.6 mm metric equivalent
How it's calculated
Tap drill = major diameter − (0.01299 × %thread) / TPI → 0.1250 − (0.01299 × 75) / 44 = 0.1029"
The nearest standard drill above that is #37 at 0.1040".
All engagement percentages
| % thread | Exact hole | Inch drill | Metric equivalent |
|---|---|---|---|
| 50% | 0.1102" | #35 (0.1100") | 2.8 mm |
| 65% | 0.1058" | #36 (0.1065") | 2.7 mm |
| 75% | 0.1029" | #37 (0.1040") | 2.6 mm |
| 85% | 0.0999" | #39 (0.0995") | 2.5 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.