#29 drill bit size
0.136 in
3.45 mm · number drill · tapping drill for 8-32, 8-36
| Inches | 0.136 in |
| Millimetres | 3.45 mm |
| Nearest metric drill | 3.5 mm |
| System | Number (#1 to #60) |
| Taps | 8-32, 8-36 |
What #29 means
A bit marked #29 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 #29:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.098 in larger |
| fractional | 9/64" — 0.1406 in | 0.0046 in larger |
| metric | 3.5 mm | 0.046 mm larger |
The closest substitute is 0.0046 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 #29 is for
#29 is the standard tapping drill for 8-32 and 8-36 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 8-32 works out at 0.1336 inches, and #29 at 0.136 is the nearest drill that exists.
What gets drilled at 0.136 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 |
|---|---|---|
| #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 |
| #27 | 0.144 in | 3.66 mm |
Frequently asked questions
What size is a #29 drill bit?
0.136 inches, which is 3.45 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 #29 drill bit in mm?
3.45 mm. A metric index will offer 3.5 mm as the nearest stocked size, which is 0.046 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
What tap does a #29 drill bit go with?
8-32, 8-36 at the standard 75% thread. Both of those come out at a theoretical diameter this drill is the nearest stocked size to.
What is the next size up from #29?
#28 at 0.1405 inches — 0.0045 inches larger. Below it is #30 at 0.1285.
Other sizes
- #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
- 5/32" drill bit — 0.1563 in, 3.97 mm