7/8" drill size
A 7/8 in drill is 0.8750 in (22.22 mm). It is the standard tap drill for 1-8 UNC; the nearest metric drill is 22.2 mm.
7/8" at a glance
Decimal, metric and the nearest sizes in the other series.
Nearest metric drills
Metric drills step by 0.05 mm below 3 mm and by 0.1 mm from 3 mm. Difference is metric minus inch size.
| Metric drill | Inch | Difference | In inches | Hole |
|---|---|---|---|---|
| 22.2 mm | 0.8740" | −0.025 mm | −0.0010" | Smaller |
| 22.3 mm | 0.8780" | +0.075 mm | +0.0030" | Larger |
Nearby inch drills
The next size down and up in each inch series, so you can pick a substitute from the drawer.
Threads a 7/8" drill can tap
Threads from the tap tables on this site that this drill can tap, with the thread percentage it leaves (55–85 % shown).
Clearance for screws and bolts
Bolts and screws a 7/8" hole clears, with the diametral clearance and the gap each side. Metric sizes are compared with ISO 273.
| Fastener | Diameter | Clearance | Per side | ISO 273, metric only |
|---|---|---|---|---|
| M20 bolt | 20 mm | 2.22 mm | 1.11 mm | Normal fit (normal 22, loose 24 mm) |
| M22 bolt | 22 mm | 0.22 mm | 0.11 mm | Tighter than close fit (23 mm) |
Inch clearance is the drill size minus the basic major diameter. A drilled hole usually cuts slightly oversize.
Fractional drill index
Every size in the series, holes drawn to scale.
Common questions
What size is a 7/8 in drill?
A 7/8 in drill is 0.8750 in, which is 22.22 mm (22.2250 mm exactly).
What is the metric equivalent of a 7/8 in drill?
The nearest metric drill is 22.2 mm, 0.025 mm smaller. The other close size is 22.3 mm.
What tap uses a 7/8 in drill?
A 7/8 in drill is the standard tap drill for 1-8 UNC (about 77 % thread).
What does a 7/8 in drill clear?
It clears a M22 bolt with 0.22 mm total clearance (0.11 mm per side); for metric bolts: tighter than close fit.