49/64" drill bit size
0.7656 in
19.45 mm · fractional drill · tapping drill for 7/8-9
| Inches | 0.7656 in |
| Millimetres | 19.45 mm |
| Nearest metric drill | 19.4 mm |
| System | Fractional (64ths) |
| Taps | 7/8-9 |
What 49/64" means
49/64" 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 49/64":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.5376 in smaller |
| letter | Z — 0.413 in | 0.3526 in smaller |
| metric | 19.4 mm | 0.047 mm smaller |
The closest substitute is 0.3526 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 49/64" is for
49/64" is the standard tapping drill for 7/8-9 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 7/8-9 works out at 0.7668 inches, and 49/64" at 0.7656 is the nearest drill that exists.
What gets drilled at 0.7656 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 |
|---|---|---|
| 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 |
| 51/64" | 0.7969 in | 20.24 mm |
| 13/16" | 0.8125 in | 20.64 mm |
Frequently asked questions
What size is a 49/64" drill bit?
0.7656 inches, which is 19.45 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 49/64" drill bit in mm?
19.45 mm. A metric index will offer 19.4 mm as the nearest stocked size, which is 0.047 mm smaller — enough to matter when tapping and not enough to matter for a clearance hole.
What tap does a 49/64" drill bit go with?
7/8-9 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 49/64"?
25/32" at 0.7813 inches — 0.0156 inches larger. Below it is 3/4" at 0.75.
Other sizes
- 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
- 7/8" drill bit — 0.875 in, 22.23 mm
- 57/64" drill bit — 0.8906 in, 22.62 mm