#51 drill bit size
0.067 in
1.7 mm · number drill
| Inches | 0.067 in |
| Millimetres | 1.7 mm |
| Nearest metric drill | 1.7 mm |
| System | Number (#1 to #60) |
What #51 means
A bit marked #51 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 #51:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.167 in larger |
| fractional | 1/16" — 0.0625 in | 0.0045 in smaller |
| metric | 1.7 mm | identical |
The closest substitute is 0.0045 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 0.067 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 |
|---|---|---|
| #53 | 0.0595 in | 1.51 mm |
| 1/16" | 0.0625 in | 1.59 mm |
| #52 | 0.0635 in | 1.61 mm |
| #51 | 0.067 in | 1.7 mm |
| #50 | 0.07 in | 1.78 mm |
| #49 | 0.073 in | 1.85 mm |
| #48 | 0.076 in | 1.93 mm |
Frequently asked questions
What size is a #51 drill bit?
0.067 inches, which is 1.7 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 #51 drill bit in mm?
1.7 mm. A metric index will offer 1.7 mm as the nearest stocked size, which is near enough identical.
Is #51 a tapping drill size?
Not for any of the unified threads on this site. The next size up, #50, is the tapping drill for 2-56 and 2-64.
What is the next size up from #51?
#50 at 0.07 inches — 0.003 inches larger. Below it is #52 at 0.0635.
Other sizes
- #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
- 5/64" drill bit — 0.0781 in, 1.98 mm
- #47 drill bit — 0.0785 in, 1.99 mm
- #46 drill bit — 0.081 in, 2.06 mm
- #45 drill bit — 0.082 in, 2.08 mm
- #44 drill bit — 0.086 in, 2.18 mm