45/64" drill bit size
0.7031 in
17.86 mm · fractional drill
| Inches | 0.7031 in |
| Millimetres | 17.86 mm |
| Nearest metric drill | 17.9 mm |
| System | Fractional (64ths) |
What 45/64" means
45/64" 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 45/64":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.4751 in smaller |
| letter | Z — 0.413 in | 0.2901 in smaller |
| metric | 17.9 mm | 0.041 mm larger |
The closest substitute is 0.2901 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 gets drilled at 0.7031 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 |
|---|---|---|
| 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 |
| 23/32" | 0.7188 in | 18.26 mm |
| 47/64" | 0.7344 in | 18.65 mm |
| 3/4" | 0.75 in | 19.05 mm |
Frequently asked questions
What size is a 45/64" drill bit?
0.7031 inches, which is 17.86 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 45/64" drill bit in mm?
17.86 mm. A metric index will offer 17.9 mm as the nearest stocked size, which is 0.041 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
Is 45/64" a tapping drill size?
Not for any of the unified threads on this site. It sits between the sizes the standard taps call for, so it is a clearance or pilot drill rather than a tapping one.
What is the next size up from 45/64"?
23/32" at 0.7188 inches — 0.0156 inches larger. Below it is 11/16" at 0.6875.
Other sizes
- 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
- 51/64" drill bit — 0.7969 in, 20.24 mm
- 13/16" drill bit — 0.8125 in, 20.64 mm
- 53/64" drill bit — 0.8281 in, 21.03 mm