#8 Drill Bit Size and Diameter
A #8 drill bit measures 0.1990 in
5.05 mm · number-size drill · gauge bit, not the 8-32 tap drill
The #8 is a numbered drill bit in the American gauge series, measuring 0.1990 inches (5.05 mm). It sits between a #9 bit (0.1960 in) and a #7 bit (0.2010 in) — just 0.002 in under the #7. Careful: "#8" here is the bit gauge — the 8-32 screw thread uses a #29 tap drill.
At a glance
| Drill size | #8 |
|---|---|
| Diameter | 0.1990 in |
| Millimetres | 5.05 mm |
| Series | Number drill (gauge) 1–97 |
| Closest fractional | 13/64 in (0.2031 in, slightly larger) |
What the #8 is used for
#8 is not the tap drill for an 8-32 thread. For 8-32 tapping use a #29 bit (0.1360 in). The #8 bit (0.1990 in) works as a close clearance hole for #8 screws and a 1/4-20 tap alternative in soft metal.
If you came for the 8-32 tap drill, that is the #29 bit — related card below. The #8 gauge bit is a niche size used for specific clearance fits.
Related sizes
Other number drill bits
The neighbourhood of the #8 in the gauge series: