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#3-48 tap drill size
Use a #47 drill (.0785 in / 1.99 mm) to tap #3-48 UNC. That gives about 76% thread engagement. Closest metric drill: 2 mm.
#3-48 thread specifications
| Thread | #3-48 UNC (coarse) |
|---|---|
| Major (nominal) diameter | .0990 in / 2.52 mm |
| Threads per inch | 48 (pitch 0.529 mm) |
| Theoretical drill for 75% thread | .0787 in (2.00 mm) |
| Recommended tap drill | #47 = .0785 in |
Alternative drills and % of thread
Any of these drills will tap #3-48. Smaller drills give more thread but make tapping harder and raise the risk of breaking the tap, especially in stainless steel and in small sizes. 60–65% thread is common in tough materials. 75% is the general-purpose standard.
| Drill | Inch | mm | % thread |
|---|---|---|---|
| #48 | .0760 in | 1.93 | 85% |
| 5/64 | .0781 in | 1.98 | 77% |
| #47 | .0785 in | 1.99 | 76% |
| #46 | .0810 in | 2.06 | 67% |
| #45 | .0820 in | 2.08 | 63% |
Tips for tapping #3-48
- Use cutting fluid, and with a hand tap back off about half a turn every turn or two to break the chip. Aluminium and soft materials are the exception: they tap cleanly with spiral-point taps.
- For blind holes, drill deeper than the thread you need. Allow at least 3–4 pitches beyond the last full thread for a plug tap (0.083" for 48 TPI).
- Thread engagement of 1–1.5 × the diameter (2.5–3.8 mm) is enough for most steel parts. Softer materials need more.