#33 drill bit size
0.113 in
2.87 mm · number drill · tapping drill for 6-40
| Inches | 0.113 in |
| Millimetres | 2.87 mm |
| Nearest metric drill | 2.9 mm |
| System | Number (#1 to #60) |
| Taps | 6-40 |
What #33 means
A bit marked #33 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 #33:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.121 in larger |
| fractional | 7/64" — 0.1094 in | 0.0036 in smaller |
| metric | 2.9 mm | 0.03 mm larger |
The closest substitute is 0.0036 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 #33 is for
#33 is the standard tapping drill for 6-40 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 6-40 works out at 0.1136 inches, and #33 at 0.113 is the nearest drill that exists.
What gets drilled at 0.113 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 |
|---|---|---|
| 7/64" | 0.1094 in | 2.78 mm |
| #35 | 0.11 in | 2.79 mm |
| #34 | 0.111 in | 2.82 mm |
| #33 | 0.113 in | 2.87 mm |
| #32 | 0.116 in | 2.95 mm |
| #31 | 0.12 in | 3.05 mm |
| 1/8" | 0.125 in | 3.18 mm |
Frequently asked questions
What size is a #33 drill bit?
0.113 inches, which is 2.87 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 #33 drill bit in mm?
2.87 mm. A metric index will offer 2.9 mm as the nearest stocked size, which is 0.03 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
What tap does a #33 drill bit go with?
6-40 at the standard 75% thread. That thread comes out at a theoretical diameter this drill is the nearest stocked size to.
What is the next size up from #33?
#32 at 0.116 inches — 0.003 inches larger. Below it is #34 at 0.111.
Other sizes
- #32 drill bit — 0.116 in, 2.95 mm
- #31 drill bit — 0.12 in, 3.05 mm
- 1/8" drill bit — 0.125 in, 3.18 mm
- #30 drill bit — 0.1285 in, 3.26 mm
- #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