9/64" drill bit size
0.1406 in
3.57 mm · fractional drill
| Inches | 0.1406 in |
| Millimetres | 3.57 mm |
| Nearest metric drill | 3.6 mm |
| System | Fractional (64ths) |
What 9/64" means
9/64" 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 9/64":
| System | Nearest size | Difference |
|---|---|---|
| number | #28 — 0.1405 in | 0.0001 in smaller |
| letter | A — 0.234 in | 0.0934 in larger |
| metric | 3.6 mm | 0.028 mm larger |
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 0.1406 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 |
|---|---|---|
| #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 |
| #26 | 0.147 in | 3.73 mm |
| #25 | 0.1495 in | 3.8 mm |
Frequently asked questions
What size is a 9/64" drill bit?
0.1406 inches, which is 3.57 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 9/64" drill bit in mm?
3.57 mm. A metric index will offer 3.6 mm as the nearest stocked size, which is 0.028 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
Is 9/64" 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 9/64"?
#27 at 0.144 inches — 0.0034 inches larger. Below it is #28 at 0.1405.
Other sizes
- #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
- #22 drill bit — 0.157 in, 3.99 mm
- #21 drill bit — 0.159 in, 4.04 mm