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#21 drill bit size
#21 drill = .1590 in = 4.04 mm. Closest metric drill: 4 mm.
Taps that use a #21 drill
- #10-32 UNF: about 76% thread
Nearby drill sizes
| Drill | Type | Inch | mm | Difference |
|---|---|---|---|---|
| #24 | number | .1520 in | 3.861 | -7.0 thou |
| #23 | number | .1540 in | 3.912 | -5.0 thou |
| 5/32 | fraction | .1563 in | 3.969 | -2.8 thou |
| #22 | number | .1570 in | 3.988 | -2.0 thou |
| #21 | number | .1590 in | 4.039 | 0.0 thou |
| #20 | number | .1610 in | 4.089 | 2.0 thou |
| #19 | number | .1660 in | 4.216 | 7.0 thou |
| #18 | number | .1695 in | 4.305 | 10.5 thou |
| 11/64 | fraction | .1719 in | 4.366 | 12.9 thou |
1 thou = 0.001 in = 0.0254 mm. Drills a few thou apart are usually interchangeable for clearance holes, but not for tap drills or reamer pilots.