#51 drill size
A #51 drill is 0.0670 in (1.70 mm). It sits between #52 and #50 in the number series; the nearest metric drill is 1.7 mm.
#51 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 |
|---|---|---|---|---|
| 1.7 mm | 0.0669" | −0.002 mm | −0.0001" | Smaller |
| 1.75 mm | 0.0689" | +0.048 mm | +0.0019" | Larger |
Nearby inch drills
The next size down and up in each inch series, so you can pick a substitute from the drawer.
Threads a #51 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).
Clearance for screws and bolts
Bolts and screws a #51 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 |
|---|---|---|---|---|
| M1.6 bolt | 1.6 mm | 0.10 mm | 0.05 mm | Close fit (close 1.7, normal 1.8 mm) |
Inch clearance is the drill size minus the basic major diameter. A drilled hole usually cuts slightly oversize.
Number drill index
Every size in the series, holes drawn to scale.
Common questions
What size is a #51 drill?
A #51 drill is 0.0670 in, which is 1.70 mm (1.7018 mm exactly).
What is the metric equivalent of a #51 drill?
The nearest metric drill is 1.7 mm, 0.002 mm smaller. The other close size is 1.75 mm.
What thread can I tap with a #51 drill?
It leaves about 82 % thread in #2-56 UNC and 57 % in M2 × 0.4.
Which fractional drill is closest to #51?
1/16 in (0.0625 in) is the closest, 0.0045 in smaller.
What does a #51 drill clear?
It clears a M1.6 bolt with 0.10 mm total clearance (0.05 mm per side); for metric bolts: close fit.