#30 drill bit size
0.1285 in
3.26 mm · number drill
| Inches | 0.1285 in |
| Millimetres | 3.26 mm |
| Nearest metric drill | 3.3 mm |
| System | Number (#1 to #60) |
What #30 means
A bit marked #30 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 #30:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.1055 in larger |
| fractional | 1/8" — 0.125 in | 0.0035 in smaller |
| metric | 3.3 mm | 0.036 mm larger |
The closest substitute is 0.0035 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 0.1285 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 |
|---|---|---|
| #32 | 0.116 in | 2.95 mm |
| #31 | 0.12 in | 3.05 mm |
| 1/8" | 0.125 in | 3.18 mm |
| #30 | 0.1285 in | 3.26 mm |
| #29 | 0.136 in | 3.45 mm |
| #28 | 0.1405 in | 3.57 mm |
| 9/64" | 0.1406 in | 3.57 mm |
Frequently asked questions
What size is a #30 drill bit?
0.1285 inches, which is 3.26 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 #30 drill bit in mm?
3.26 mm. A metric index will offer 3.3 mm as the nearest stocked size, which is 0.036 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
Is #30 a tapping drill size?
Not for any of the unified threads on this site. The next size up, #29, is the tapping drill for 8-32 and 8-36.
What is the next size up from #30?
#29 at 0.136 inches — 0.0075 inches larger. Below it is 1/8" at 0.125.
Other sizes
- #29 drill bit — 0.136 in, 3.45 mm
- #28 drill bit — 0.1405 in, 3.57 mm
- 9/64" drill bit — 0.1406 in, 3.57 mm
- #27 drill bit — 0.144 in, 3.66 mm
- #26 drill bit — 0.147 in, 3.73 mm
- #25 drill bit — 0.1495 in, 3.8 mm
- #24 drill bit — 0.152 in, 3.86 mm
- #23 drill bit — 0.154 in, 3.91 mm