#8 drill bit size
0.199 in
5.05 mm · number drill
| Inches | 0.199 in |
| Millimetres | 5.05 mm |
| Nearest metric drill | 5.1 mm |
| System | Number (#1 to #60) |
What #8 means
A bit marked #8 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 #8:
| System | Nearest size | Difference |
|---|---|---|
| letter | A — 0.234 in | 0.035 in larger |
| fractional | 13/64" — 0.2031 in | 0.0041 in larger |
| metric | 5.1 mm | 0.045 mm larger |
The closest substitute is 0.0041 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 0.199 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 |
|---|---|---|
| #11 | 0.191 in | 4.85 mm |
| #10 | 0.1935 in | 4.91 mm |
| #9 | 0.196 in | 4.98 mm |
| #8 | 0.199 in | 5.05 mm |
| #7 | 0.201 in | 5.11 mm |
| 13/64" | 0.2031 in | 5.16 mm |
| #6 | 0.204 in | 5.18 mm |
Frequently asked questions
What size is a #8 drill bit?
0.199 inches, which is 5.05 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 #8 drill bit in mm?
5.05 mm. A metric index will offer 5.1 mm as the nearest stocked size, which is 0.045 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
Is #8 a tapping drill size?
Not for any of the unified threads on this site. The next size up, #7, is the tapping drill for 1/4-20.
What is the next size up from #8?
#7 at 0.201 inches — 0.002 inches larger. Below it is #9 at 0.196.
Other sizes
- #7 drill bit — 0.201 in, 5.11 mm
- 13/64" drill bit — 0.2031 in, 5.16 mm
- #6 drill bit — 0.204 in, 5.18 mm
- #5 drill bit — 0.2055 in, 5.22 mm
- #4 drill bit — 0.209 in, 5.31 mm
- #3 drill bit — 0.213 in, 5.41 mm
- 7/32" drill bit — 0.2188 in, 5.56 mm
- #2 drill bit — 0.221 in, 5.61 mm