#7 Drill Bit Size and Diameter
A #7 drill bit measures 0.2010 in
5.105 mm · number-size drill · used as the 1/4-20 tap drill
The #7 is a numbered drill bit in the American gauge series. At 0.2010 inches (5.105 mm) it sits between a 13/64 in bit (0.2031 in) and a #6 bit (0.2040 in). It is best known as the standard tap drill for a 1/4-20 UNC thread.
At a glance
| Drill size | #7 |
|---|---|
| Diameter | 0.2010 in |
| Millimetres | 5.105 mm |
| Series | Number drill (gauge) 1–97 |
| Closest fractional | 13/64 in (0.2031 in, slightly larger) |
What the #7 is used for
1/4-20 tap drill: drillØ = major − (pitch × 0.75) = 0.2500 − (0.0500 × 0.75) = 0.2125 in → nearest standard bit = #7 (0.2010 in)
Drilling a #7 hole before running a 1/4-20 tap leaves about 75% thread engagement — the standard strength fit. In soft aluminium a 13/64 in bit gives a slightly looser, safer thread.
Related sizes
Other number drill bits
The neighbourhood of the #7 in the gauge series: