Letter K drill size
A letter K drill is 0.2810 in (7.14 mm). It sits between letter J and letter L in the letter series; the nearest metric drill is 7.1 mm.
Letter K 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 |
|---|---|---|---|---|
| 7.1 mm | 0.2795" | −0.037 mm | −0.0015" | Smaller |
| 7.2 mm | 0.2835" | +0.063 mm | +0.0025" | 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 | −0.0530" |
| 17/64" | Fractional | 0.2656" | 6.75 mm | −0.0154" |
| Letter J | Letter | 0.2770" | 7.04 mm | −0.0040" |
| Letter K | Letter | 0.2810" | 7.14 mm | this size |
| 9/32" | Fractional | 0.2812" | 7.14 mm | +0.0002" |
| Letter L | Letter | 0.2900" | 7.37 mm | +0.0090" |
Threads a Letter K drill can tap
Threads from the tap tables on this site that this drill can tap, with the thread percentage it leaves (55–85 % shown).
| Thread | Standard drill | Thread with this drill | Suits |
|---|---|---|---|
| M8 × 1 | 7 mm | 66 % | Good in steel |
| 5/16-24 UNF | I | 58 % | Hard, tough metals |
Clearance for screws and bolts
Bolts and screws a Letter K 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 |
|---|---|---|---|---|
| 1/4" bolt | 0.2500" | 0.0310" | 0.0155" | – |
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 K drill?
A letter K drill is 0.2810 in, which is 7.14 mm (7.1374 mm exactly).
What is the metric equivalent of a letter K drill?
The nearest metric drill is 7.1 mm, 0.037 mm smaller. The other close size is 7.2 mm.
What thread can I tap with a letter K drill?
It leaves about 66 % thread in M8 × 1 and 58 % in 5/16-24 UNF.
Which fractional drill is closest to letter K?
9/32 in (0.2812 in) is the closest, 0.0002 in larger.
What does a letter K drill clear?
It clears a 1/4" bolt with 0.0310" total clearance (0.0155" per side).