13/16" drill bit size
0.8125 in
20.64 mm · fractional drill · tapping drill for 7/8-14
| Inches | 0.8125 in |
| Millimetres | 20.64 mm |
| Nearest metric drill | 20.6 mm |
| System | Fractional (64ths) |
| Taps | 7/8-14 |
What 13/16" means
13/16" 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 13/16":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.5845 in smaller |
| letter | Z — 0.413 in | 0.3995 in smaller |
| metric | 20.6 mm | 0.037 mm smaller |
The closest substitute is 0.3995 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 13/16" is for
13/16" is the standard tapping drill for 7/8-14 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 7/8-14 works out at 0.8054 inches, and 13/16" at 0.8125 is the nearest drill that exists.
What gets drilled at 0.8125 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 |
|---|---|---|
| 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 |
| 53/64" | 0.8281 in | 21.03 mm |
| 27/32" | 0.8438 in | 21.43 mm |
| 55/64" | 0.8594 in | 21.83 mm |
Frequently asked questions
What size is a 13/16" drill bit?
0.8125 inches, which is 20.64 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 13/16" drill bit in mm?
20.64 mm. A metric index will offer 20.6 mm as the nearest stocked size, which is 0.037 mm smaller — enough to matter when tapping and not enough to matter for a clearance hole.
What tap does a 13/16" drill bit go with?
7/8-14 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 13/16"?
53/64" at 0.8281 inches — 0.0156 inches larger. Below it is 51/64" at 0.7969.
Other sizes
- 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
- 29/32" drill bit — 0.9063 in, 23.02 mm
- 59/64" drill bit — 0.9219 in, 23.42 mm
- 15/16" drill bit — 0.9375 in, 23.81 mm