#20 drill bit size
0.161 in
4.09 mm · number drill
| Inches | 0.161 in |
| Millimetres | 4.09 mm |
| Nearest metric drill | 4.1 mm |
| System | Number (#1 to #60) |
What #20 means
A bit marked #20 is a number drill, and the number is an index rather than a measurement — the higher the number, the smaller the bit. #1 is 0.228 inches and #60 is 0.04. That is the opposite of the fractional sizes stamped on a home set, which is why a number drill and a fraction of similar appearance can be very different holes.
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 #20:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.073 in larger |
| fractional | 5/32" — 0.1563 in | 0.0048 in smaller |
| metric | 4.1 mm | 0.011 mm larger |
The closest substitute is 0.0048 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 gets drilled at 0.161 inches
The busiest part of the number series. Tapping drills for machine screws from #4 to #12 sit in here, along with pilot holes for wood screws and clearance for small pins. If a number drill in a workshop is worn out, it is usually one of these.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| 5/32" | 0.1563 in | 3.97 mm |
| #22 | 0.157 in | 3.99 mm |
| #21 | 0.159 in | 4.04 mm |
| #20 | 0.161 in | 4.09 mm |
| #19 | 0.166 in | 4.22 mm |
| #18 | 0.1695 in | 4.31 mm |
| 11/64" | 0.1719 in | 4.37 mm |
Frequently asked questions
What size is a #20 drill bit?
0.161 inches, which is 4.09 mm. Number drills run from #1 at 0.228 inches down to #60 at 0.04, getting smaller as the number rises — the opposite of what most people expect the first time.
What is a #20 drill bit in mm?
4.09 mm. A metric index will offer 4.1 mm as the nearest stocked size, which is near enough identical.
Is #20 a tapping drill size?
Not for any of the unified threads on this site. It sits between the sizes the standard taps call for, so it is a clearance or pilot drill rather than a tapping one.
What is the next size up from #20?
#19 at 0.166 inches — 0.005 inches larger. Below it is #21 at 0.159.
Other sizes
- #19 drill bit — 0.166 in, 4.22 mm
- #18 drill bit — 0.1695 in, 4.31 mm
- 11/64" drill bit — 0.1719 in, 4.37 mm
- #17 drill bit — 0.173 in, 4.39 mm
- #16 drill bit — 0.177 in, 4.5 mm
- #15 drill bit — 0.18 in, 4.57 mm
- #14 drill bit — 0.182 in, 4.62 mm
- #13 drill bit — 0.185 in, 4.7 mm