7/8" drill bit size
0.875 in
22.23 mm · fractional drill · tapping drill for 1-8
| Inches | 0.875 in |
| Millimetres | 22.23 mm |
| Nearest metric drill | 22.2 mm |
| System | Fractional (64ths) |
| Taps | 1-8 |
What 7/8" means
7/8" 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 7/8":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.647 in smaller |
| letter | Z — 0.413 in | 0.462 in smaller |
| metric | 22.2 mm | 0.025 mm smaller |
The closest substitute is 0.462 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 7/8" is for
7/8" is the standard tapping drill for 1-8 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 1-8 works out at 0.8782 inches, and 7/8" at 0.875 is the nearest drill that exists.
What gets drilled at 0.875 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 |
|---|---|---|
| 53/64" | 0.8281 in | 21.03 mm |
| 27/32" | 0.8438 in | 21.43 mm |
| 55/64" | 0.8594 in | 21.83 mm |
| 7/8" | 0.875 in | 22.23 mm |
| 57/64" | 0.8906 in | 22.62 mm |
| 29/32" | 0.9063 in | 23.02 mm |
| 59/64" | 0.9219 in | 23.42 mm |
Frequently asked questions
What size is a 7/8" drill bit?
0.875 inches, which is 22.23 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 7/8" drill bit in mm?
22.23 mm. A metric index will offer 22.2 mm as the nearest stocked size, which is 0.025 mm smaller — enough to matter when tapping and not enough to matter for a clearance hole.
What tap does a 7/8" drill bit go with?
1-8 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 7/8"?
57/64" at 0.8906 inches — 0.0156 inches larger. Below it is 55/64" at 0.8594.
Other sizes
- 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
- 61/64" drill bit — 0.9531 in, 24.21 mm
- 31/32" drill bit — 0.9688 in, 24.61 mm
- 63/64" drill bit — 0.9844 in, 25 mm
- 1/1" drill bit — 1 in, 25.4 mm