#23 drill bit size
0.154 in
3.91 mm · number drill
| Inches | 0.154 in |
| Millimetres | 3.91 mm |
| Nearest metric drill | 3.9 mm |
| System | Number (#1 to #60) |
What #23 means
A bit marked #23 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 #23:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.08 in larger |
| fractional | 5/32" — 0.1563 in | 0.0023 in larger |
| metric | 3.9 mm | 0.012 mm smaller |
One of those is within three thousandths of an inch, which is inside the tolerance of most hand-held work — substitute it and nobody will know.
What gets drilled at 0.154 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 |
|---|---|---|
| #26 | 0.147 in | 3.73 mm |
| #25 | 0.1495 in | 3.8 mm |
| #24 | 0.152 in | 3.86 mm |
| #23 | 0.154 in | 3.91 mm |
| 5/32" | 0.1563 in | 3.97 mm |
| #22 | 0.157 in | 3.99 mm |
| #21 | 0.159 in | 4.04 mm |
Frequently asked questions
What size is a #23 drill bit?
0.154 inches, which is 3.91 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 #23 drill bit in mm?
3.91 mm. A metric index will offer 3.9 mm as the nearest stocked size, which is near enough identical.
Is #23 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 #23?
5/32" at 0.1563 inches — 0.0023 inches larger. Below it is #24 at 0.152.
Other sizes
- 5/32" drill bit — 0.1563 in, 3.97 mm
- #22 drill bit — 0.157 in, 3.99 mm
- #21 drill bit — 0.159 in, 4.04 mm
- #20 drill bit — 0.161 in, 4.09 mm
- #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