#50 drill bit size
0.07 in
1.78 mm · number drill · tapping drill for 2-56, 2-64
| Inches | 0.07 in |
| Millimetres | 1.78 mm |
| Nearest metric drill | 1.8 mm |
| System | Number (#1 to #60) |
| Taps | 2-56, 2-64 |
What #50 means
A bit marked #50 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 #50:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.164 in larger |
| fractional | 1/16" — 0.0625 in | 0.0075 in smaller |
| metric | 1.8 mm | 0.022 mm larger |
The closest substitute is 0.0075 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 #50 is for
#50 is the standard tapping drill for 2-56 and 2-64 at 75% thread engagement. That is not a coincidence of the tables: the theoretical figure for 2-56 works out at 0.0686 inches, and #50 at 0.07 is the nearest drill that exists.
What gets drilled at 0.07 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 |
|---|---|---|
| 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 |
| 5/64" | 0.0781 in | 1.98 mm |
Frequently asked questions
What size is a #50 drill bit?
0.07 inches, which is 1.78 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 #50 drill bit in mm?
1.78 mm. A metric index will offer 1.8 mm as the nearest stocked size, which is 0.022 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
What tap does a #50 drill bit go with?
2-56, 2-64 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 #50?
#49 at 0.073 inches — 0.003 inches larger. Below it is #51 at 0.067.
Other sizes
- #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
- #43 drill bit — 0.089 in, 2.26 mm