Letter B drill size
A letter B drill is 0.2380 in (6.05 mm). It sits between letter A and letter C in the letter series; the nearest metric drill is 6.0 mm.
Letter B at a glance
Decimal, metric and the nearest sizes in the other series.
Nearest metric drills
Metric drills step by 0.05 mm below 3 mm and by 0.1 mm from 3 mm. Difference is metric minus inch size.
| Metric drill | Inch | Difference | In inches | Hole |
|---|---|---|---|---|
| 6.0 mm | 0.2362" | −0.045 mm | −0.0018" | Smaller |
| 6.1 mm | 0.2402" | +0.055 mm | +0.0022" | Larger |
Nearby inch drills
The next size down and up in each inch series, so you can pick a substitute from the drawer.
| Drill | Series | Inch | mm | Difference |
|---|---|---|---|---|
| #1 | Number | 0.2280" | 5.79 mm | −0.0100" |
| Letter A | Letter | 0.2340" | 5.94 mm | −0.0040" |
| 15/64" | Fractional | 0.2344" | 5.95 mm | −0.0036" |
| Letter B | Letter | 0.2380" | 6.05 mm | this size |
| Letter C | Letter | 0.2420" | 6.15 mm | +0.0040" |
| 1/4" | Fractional | 0.2500" | 6.35 mm | +0.0120" |
Threads a Letter B drill can tap
No thread in the tap tables on this site falls between 55 and 85 % thread with this drill, so it is not a useful tap drill for them. Drills this size are mostly used for clearance, pilot and pin holes.
Clearance for screws and bolts
Bolts and screws a Letter B hole clears, with the diametral clearance and the gap each side. Metric sizes are compared with ISO 273.
| Fastener | Diameter | Clearance | Per side | ISO 273, metric only |
|---|---|---|---|---|
| #10 screw | 0.1900" | 0.0480" | 0.0240" | – |
| #12 screw | 0.2160" | 0.0220" | 0.0110" | – |
| M6 bolt | 6 mm | 0.05 mm | 0.02 mm | Tighter than close fit (6.4 mm) |
Inch clearance is the drill size minus the basic major diameter. A drilled hole usually cuts slightly oversize.
Letter drill index
Every size in the series, holes drawn to scale.
Common questions
What size is a letter B drill?
A letter B drill is 0.2380 in, which is 6.05 mm (6.0452 mm exactly).
What is the metric equivalent of a letter B drill?
The nearest metric drill is 6.0 mm, 0.045 mm smaller. The other close size is 6.1 mm.
Which fractional drill is closest to letter B?
15/64 in (0.2344 in) is the closest, 0.0036 in smaller.
What does a letter B drill clear?
It clears a M6 bolt with 0.05 mm total clearance (0.02 mm per side); for metric bolts: tighter than close fit.