#3 drill bit size
0.213 in
5.41 mm · number drill · tapping drill for 1/4-28
| Inches | 0.213 in |
| Millimetres | 5.41 mm |
| Nearest metric drill | 5.4 mm |
| System | Number (#1 to #60) |
| Taps | 1/4-28 |
What #3 means
A bit marked #3 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 #3:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.021 in larger |
| fractional | 7/32" — 0.2188 in | 0.0058 in larger |
| metric | 5.4 mm | 0.01 mm smaller |
The closest substitute is 0.0058 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 #3 is for
#3 is the standard tapping drill for 1/4-28 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 1/4-28 works out at 0.2152 inches, and #3 at 0.213 is the nearest drill that exists.
What gets drilled at 0.213 inches
Where the quarter-inch and five-sixteenths taps are drilled, and where clearance holes for small bolts begin. The three drill systems overlap most densely across this band, which is why a bit here is the one most often picked up and misidentified.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| #6 | 0.204 in | 5.18 mm |
| #5 | 0.2055 in | 5.22 mm |
| #4 | 0.209 in | 5.31 mm |
| #3 | 0.213 in | 5.41 mm |
| 7/32" | 0.2188 in | 5.56 mm |
| #2 | 0.221 in | 5.61 mm |
| #1 | 0.228 in | 5.79 mm |
Frequently asked questions
What size is a #3 drill bit?
0.213 inches, which is 5.41 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 #3 drill bit in mm?
5.41 mm. A metric index will offer 5.4 mm as the nearest stocked size, which is near enough identical.
What tap does a #3 drill bit go with?
1/4-28 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 #3?
7/32" at 0.2188 inches — 0.0058 inches larger. Below it is #4 at 0.209.
Other sizes
- 7/32" drill bit — 0.2188 in, 5.56 mm
- #2 drill bit — 0.221 in, 5.61 mm
- #1 drill bit — 0.228 in, 5.79 mm
- A drill bit — 0.234 in, 5.94 mm
- 15/64" drill bit — 0.2344 in, 5.95 mm
- B drill bit — 0.238 in, 6.05 mm
- C drill bit — 0.242 in, 6.15 mm
- D drill bit — 0.246 in, 6.25 mm