3/8" drill bit size
0.375 in
9.52 mm · fractional drill
| Inches | 0.375 in |
| Millimetres | 9.52 mm |
| Nearest metric drill | 9.5 mm |
| System | Fractional (64ths) |
What 3/8" means
3/8" is a fractional drill, stepping in 64ths of an inch. Fractional sizes are the coarsest of the three systems, which is why a fractional set alone cannot hit most tapping sizes and why number and letter drills exist at all.
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 3/8":
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.147 in smaller |
| letter | V — 0.377 in | 0.002 in larger |
| metric | 9.5 mm | 0.025 mm smaller |
One of those is within three thousandths of an inch, which is inside the tolerance of most hand-held work — substitute it and nobody will know.
What gets drilled at 0.375 inches
Clearance holes for bolts up to about half an inch, and tapping drills for the larger unified threads. Above a quarter inch a hand drill starts to want two hands and a slower speed, and the bit wants a pilot hole.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| T | 0.358 in | 9.09 mm |
| 23/64" | 0.3594 in | 9.13 mm |
| U | 0.368 in | 9.35 mm |
| 3/8" | 0.375 in | 9.52 mm |
| V | 0.377 in | 9.58 mm |
| W | 0.386 in | 9.8 mm |
| 25/64" | 0.3906 in | 9.92 mm |
Frequently asked questions
What size is a 3/8" drill bit?
0.375 inches, which is 9.52 mm. Fractional drills step in 64ths of an inch, which is the coarsest of the three systems and the one most home sets contain.
What is a 3/8" drill bit in mm?
9.52 mm. A metric index will offer 9.5 mm as the nearest stocked size, which is 0.025 mm smaller — enough to matter when tapping and not enough to matter for a clearance hole.
Is 3/8" a tapping drill size?
Not for any of the unified threads on this site. It sits between the sizes the standard taps call for, so it is a clearance or pilot drill rather than a tapping one.
What is the next size up from 3/8"?
V at 0.377 inches — 0.002 inches larger. Below it is U at 0.368.
Other sizes
- V drill bit — 0.377 in, 9.58 mm
- W drill bit — 0.386 in, 9.8 mm
- 25/64" drill bit — 0.3906 in, 9.92 mm
- X drill bit — 0.397 in, 10.08 mm
- Y drill bit — 0.404 in, 10.26 mm
- 13/32" drill bit — 0.4063 in, 10.32 mm
- Z drill bit — 0.413 in, 10.49 mm
- 27/64" drill bit — 0.4219 in, 10.72 mm