31/64" drill bit size
0.4844 in
12.3 mm · fractional drill · tapping drill for 9/16-12
| Inches | 0.4844 in |
| Millimetres | 12.3 mm |
| Nearest metric drill | 12.3 mm |
| System | Fractional (64ths) |
| Taps | 9/16-12 |
What 31/64" means
31/64" 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 31/64":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.2564 in smaller |
| letter | Z — 0.413 in | 0.0714 in smaller |
| metric | 12.3 mm | identical |
The closest substitute is 0.0714 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 31/64" is for
31/64" is the standard tapping drill for 9/16-12 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 9/16-12 works out at 0.4813 inches, and 31/64" at 0.4844 is the nearest drill that exists.
What gets drilled at 0.4844 inches
Clearance holes for bolts up to about half an inch, and tapping drills for the larger unified threads. Above a quarter inch a hand drill starts to want two hands and a slower speed, and the bit wants a pilot hole.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| 7/16" | 0.4375 in | 11.11 mm |
| 29/64" | 0.4531 in | 11.51 mm |
| 15/32" | 0.4688 in | 11.91 mm |
| 31/64" | 0.4844 in | 12.3 mm |
| 1/2" | 0.5 in | 12.7 mm |
| 33/64" | 0.5156 in | 13.1 mm |
| 17/32" | 0.5313 in | 13.49 mm |
Frequently asked questions
What size is a 31/64" drill bit?
0.4844 inches, which is 12.3 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 31/64" drill bit in mm?
12.3 mm. A metric index will offer 12.3 mm as the nearest stocked size, which is near enough identical.
What tap does a 31/64" drill bit go with?
9/16-12 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 31/64"?
1/2" at 0.5 inches — 0.0156 inches larger. Below it is 15/32" at 0.4688.
Other sizes
- 1/2" drill bit — 0.5 in, 12.7 mm
- 33/64" drill bit — 0.5156 in, 13.1 mm
- 17/32" drill bit — 0.5313 in, 13.49 mm
- 35/64" drill bit — 0.5469 in, 13.89 mm
- 9/16" drill bit — 0.5625 in, 14.29 mm
- 37/64" drill bit — 0.5781 in, 14.68 mm
- 19/32" drill bit — 0.5938 in, 15.08 mm
- 39/64" drill bit — 0.6094 in, 15.48 mm