A drill bit size
0.234 in
5.94 mm · letter drill
| Inches | 0.234 in |
| Millimetres | 5.94 mm |
| Nearest metric drill | 5.9 mm |
| System | Letter (A to Z) |
What A means
A bit marked A is a letter drill. Letters run A to Z and get larger as they advance, covering 0.234 to 0.413 inches — the gap between the largest number drill and the point where fractional sizes become fine enough to be useful.
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 A:
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.006 in smaller |
| fractional | 15/64" — 0.2344 in | 0.0004 in larger |
| metric | 5.9 mm | 0.044 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 0.234 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 |
|---|---|---|
| 7/32" | 0.2188 in | 5.56 mm |
| #2 | 0.221 in | 5.61 mm |
| #1 | 0.228 in | 5.79 mm |
| A | 0.234 in | 5.94 mm |
| 15/64" | 0.2344 in | 5.95 mm |
| B | 0.238 in | 6.05 mm |
| C | 0.242 in | 6.15 mm |
Frequently asked questions
What size is a A drill bit?
0.234 inches, which is 5.94 mm. Letter drills run A to Z and get larger as the letter advances, filling the gap between the largest number drill and the fractional sizes.
What is a A drill bit in mm?
5.94 mm. A metric index will offer 5.9 mm as the nearest stocked size, which is 0.044 mm smaller — enough to matter when tapping and not enough to matter for a clearance hole.
Is A 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 A?
15/64" at 0.2344 inches — 0.0004 inches larger. Below it is #1 at 0.228.
Other sizes
- 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
- E drill bit — 0.25 in, 6.35 mm
- 1/4" drill bit — 0.25 in, 6.35 mm
- F drill bit — 0.257 in, 6.53 mm
- G drill bit — 0.261 in, 6.63 mm