#8 drill size
A #8 drill is 0.1990 in (5.05 mm). It sits between #9 and #7 in the number series; the nearest metric drill is 5.1 mm.
#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 |
|---|---|---|---|---|
| 5.0 mm | 0.1969" | −0.055 mm | −0.0021" | Smaller |
| 5.1 mm | 0.2008" | +0.045 mm | +0.0018" | 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 #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).
| Thread | Standard drill | Thread with this drill | Suits |
|---|---|---|---|
| M6 × 1 | 5 mm | 73 % | Good in steel |
| 1/4-20 UNC | #7 | 79 % | Soft metals, plastics |
Clearance for screws and bolts
Bolts and screws a #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 |
|---|---|---|---|---|
| #6 screw | 0.1380" | 0.0610" | 0.0305" | – |
| #8 screw | 0.1640" | 0.0350" | 0.0175" | – |
| #10 screw | 0.1900" | 0.0090" | 0.0045" | – |
| M5 bolt | 5 mm | 0.05 mm | 0.03 mm | Tighter than close fit (5.3 mm) |
Inch clearance is the drill size minus the basic major diameter. A drilled hole usually cuts slightly oversize.
Number drill index
Every size in the series, holes drawn to scale.
Common questions
What size is a #8 drill?
A #8 drill is 0.1990 in, which is 5.05 mm (5.0546 mm exactly).
What is the metric equivalent of a #8 drill?
The nearest metric drill is 5.1 mm, 0.045 mm larger. The other close size is 5.0 mm.
What thread can I tap with a #8 drill?
It leaves about 73 % thread in M6 × 1 and 79 % in 1/4-20 UNC.
Which fractional drill is closest to #8?
13/64 in (0.2031 in) is the closest, 0.0041 in larger.
What does a #8 drill clear?
It clears a M5 bolt with 0.05 mm total clearance (0.03 mm per side); for metric bolts: tighter than close fit.