47/64" drill bit size
0.7344 in
18.65 mm · fractional drill
| Inches | 0.7344 in |
| Millimetres | 18.65 mm |
| Nearest metric drill | 18.7 mm |
| System | Fractional (64ths) |
What 47/64" means
47/64" 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 47/64":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.5064 in smaller |
| letter | Z — 0.413 in | 0.3214 in smaller |
| metric | 18.7 mm | 0.047 mm larger |
The closest substitute is 0.3214 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 0.7344 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 |
|---|---|---|
| 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 |
| 49/64" | 0.7656 in | 19.45 mm |
| 25/32" | 0.7813 in | 19.84 mm |
Frequently asked questions
What size is a 47/64" drill bit?
0.7344 inches, which is 18.65 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 47/64" drill bit in mm?
18.65 mm. A metric index will offer 18.7 mm as the nearest stocked size, which is 0.047 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
Is 47/64" 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 47/64"?
3/4" at 0.75 inches — 0.0156 inches larger. Below it is 23/32" at 0.7188.
Other sizes
- 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
- 27/32" drill bit — 0.8438 in, 21.43 mm
- 55/64" drill bit — 0.8594 in, 21.83 mm