#55 drill bit size
0.052 in
1.32 mm · number drill
| Inches | 0.052 in |
| Millimetres | 1.32 mm |
| Nearest metric drill | 1.3 mm |
| System | Number (#1 to #60) |
What #55 means
A bit marked #55 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 #55:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.182 in larger |
| fractional | 3/64" — 0.0469 in | 0.0051 in smaller |
| metric | 1.3 mm | 0.021 mm smaller |
The closest substitute is 0.0051 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 0.052 inches
This is circuit-board and small-pin range — component leads, header pins, the holes a hobbyist drills in perfboard. It is also where the smallest machine-screw taps live, so a drill here is as likely to be preparing a thread as clearing a wire.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| #57 | 0.043 in | 1.09 mm |
| #56 | 0.0465 in | 1.18 mm |
| 3/64" | 0.0469 in | 1.19 mm |
| #55 | 0.052 in | 1.32 mm |
| #54 | 0.055 in | 1.4 mm |
| #53 | 0.0595 in | 1.51 mm |
| 1/16" | 0.0625 in | 1.59 mm |
Frequently asked questions
What size is a #55 drill bit?
0.052 inches, which is 1.32 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 #55 drill bit in mm?
1.32 mm. A metric index will offer 1.3 mm as the nearest stocked size, which is 0.021 mm smaller — enough to matter when tapping and not enough to matter for a clearance hole.
Is #55 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 #55?
#54 at 0.055 inches — 0.003 inches larger. Below it is 3/64" at 0.0469.
Other sizes
- #54 drill bit — 0.055 in, 1.4 mm
- #53 drill bit — 0.0595 in, 1.51 mm
- 1/16" drill bit — 0.0625 in, 1.59 mm
- #52 drill bit — 0.0635 in, 1.61 mm
- #51 drill bit — 0.067 in, 1.7 mm
- #50 drill bit — 0.07 in, 1.78 mm
- #49 drill bit — 0.073 in, 1.85 mm
- #48 drill bit — 0.076 in, 1.93 mm