33/64" drill bit size
0.5156 in
13.1 mm · fractional drill · tapping drill for 9/16-18
| Inches | 0.5156 in |
| Millimetres | 13.1 mm |
| Nearest metric drill | 13.1 mm |
| System | Fractional (64ths) |
| Taps | 9/16-18 |
What 33/64" means
33/64" 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 33/64":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.2876 in smaller |
| letter | Z — 0.413 in | 0.1026 in smaller |
| metric | 13.1 mm | identical |
The closest substitute is 0.1026 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 33/64" is for
33/64" is the standard tapping drill for 9/16-18 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 9/16-18 works out at 0.5084 inches, and 33/64" at 0.5156 is the nearest drill that exists.
What gets drilled at 0.5156 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 |
|---|---|---|
| 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 |
| 35/64" | 0.5469 in | 13.89 mm |
| 9/16" | 0.5625 in | 14.29 mm |
Frequently asked questions
What size is a 33/64" drill bit?
0.5156 inches, which is 13.1 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 33/64" drill bit in mm?
13.1 mm. A metric index will offer 13.1 mm as the nearest stocked size, which is near enough identical.
What tap does a 33/64" drill bit go with?
9/16-18 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 33/64"?
17/32" at 0.5313 inches — 0.0156 inches larger. Below it is 1/2" at 0.5.
Other sizes
- 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
- 5/8" drill bit — 0.625 in, 15.88 mm
- 41/64" drill bit — 0.6406 in, 16.27 mm