Letter G drill size
A letter G drill is 0.2610 in (6.63 mm). It sits between letter F and letter H in the letter series; the nearest metric drill is 6.6 mm.
Letter G 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 |
|---|---|---|---|---|
| 6.6 mm | 0.2598" | −0.029 mm | −0.0012" | Smaller |
| 6.7 mm | 0.2638" | +0.071 mm | +0.0028" | 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 | −0.0330" |
| 1/4" | Fractional | 0.2500" | 6.35 mm | −0.0110" |
| Letter F | Letter | 0.2570" | 6.53 mm | −0.0040" |
| Letter G | Letter | 0.2610" | 6.63 mm | this size |
| 17/64" | Fractional | 0.2656" | 6.75 mm | +0.0046" |
| Letter H | Letter | 0.2660" | 6.76 mm | +0.0050" |
Threads a Letter G 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 |
|---|---|---|---|
| 5/16-18 UNC | F | 71 % | Good in steel |
| M8 × 1.25 | 6.8 mm | 84 % | Soft metals, plastics |
Clearance for screws and bolts
Bolts and screws a Letter G 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 |
|---|---|---|---|---|
| #12 screw | 0.2160" | 0.0450" | 0.0225" | – |
| M6 bolt | 6 mm | 0.63 mm | 0.31 mm | Normal fit (normal 6.6, loose 7 mm) |
| 1/4" bolt | 0.2500" | 0.0110" | 0.0055" | – |
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 G drill?
A letter G drill is 0.2610 in, which is 6.63 mm (6.6294 mm exactly).
What is the metric equivalent of a letter G drill?
The nearest metric drill is 6.6 mm, 0.029 mm smaller. The other close size is 6.7 mm.
What thread can I tap with a letter G drill?
It leaves about 71 % thread in 5/16-18 UNC and 84 % in M8 × 1.25.
Which fractional drill is closest to letter G?
17/64 in (0.2656 in) is the closest, 0.0046 in larger.
What does a letter G drill clear?
It clears a 1/4" bolt with 0.0110" total clearance (0.0055" per side).