21/32" drill bit size
0.6563 in
16.67 mm · fractional drill · tapping drill for 3/4-10
| Inches | 0.6563 in |
| Millimetres | 16.67 mm |
| Nearest metric drill | 16.7 mm |
| System | Fractional (64ths) |
| Taps | 3/4-10 |
What 21/32" means
21/32" is a fractional drill, stepping in 64ths of an inch. Fractional sizes are the coarsest of the three systems, which is why a fractional set alone cannot hit most tapping sizes and why number and letter drills exist at all.
The same hole in the other systems
Three drill systems overlap across this range and a workshop rarely has all three. The nearest bit of each other kind to 21/32":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.4283 in smaller |
| letter | Z — 0.413 in | 0.2433 in smaller |
| metric | 16.7 mm | 0.031 mm larger |
The closest substitute is 0.2433 inches away. For a clearance hole that is nothing; for a tapping hole it moves the thread engagement by several per cent, which is the difference between an easy tap and a broken one.
What 21/32" is for
21/32" is the standard tapping drill for 3/4-10 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 3/4-10 works out at 0.6526 inches, and 21/32" at 0.6563 is the nearest drill that exists.
What gets drilled at 0.6563 inches
Half an inch and up is where twist drills stop being the obvious tool. A bit this size in mild steel needs a pilot, a slow speed and something to hold the work; past three-quarters of an inch most people reach for a hole saw or a step drill instead.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| 39/64" | 0.6094 in | 15.48 mm |
| 5/8" | 0.625 in | 15.88 mm |
| 41/64" | 0.6406 in | 16.27 mm |
| 21/32" | 0.6563 in | 16.67 mm |
| 43/64" | 0.6719 in | 17.07 mm |
| 11/16" | 0.6875 in | 17.46 mm |
| 45/64" | 0.7031 in | 17.86 mm |
Frequently asked questions
What size is a 21/32" drill bit?
0.6563 inches, which is 16.67 mm. Fractional drills step in 64ths of an inch, which is the coarsest of the three systems and the one most home sets contain.
What is a 21/32" drill bit in mm?
16.67 mm. A metric index will offer 16.7 mm as the nearest stocked size, which is 0.031 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
What tap does a 21/32" drill bit go with?
3/4-10 at the standard 75% thread. That thread comes out at a theoretical diameter this drill is the nearest stocked size to.
What is the next size up from 21/32"?
43/64" at 0.6719 inches — 0.0156 inches larger. Below it is 41/64" at 0.6406.
Other sizes
- 43/64" drill bit — 0.6719 in, 17.07 mm
- 11/16" drill bit — 0.6875 in, 17.46 mm
- 45/64" drill bit — 0.7031 in, 17.86 mm
- 23/32" drill bit — 0.7188 in, 18.26 mm
- 47/64" drill bit — 0.7344 in, 18.65 mm
- 3/4" drill bit — 0.75 in, 19.05 mm
- 49/64" drill bit — 0.7656 in, 19.45 mm
- 25/32" drill bit — 0.7813 in, 19.84 mm