#28 drill size
A #28 drill is 0.1405 in (3.57 mm). It sits between #29 and #27 in the number series; the nearest metric drill is 3.6 mm.
#28 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 |
|---|---|---|---|---|
| 3.5 mm | 0.1378" | −0.069 mm | −0.0027" | Smaller |
| 3.6 mm | 0.1417" | +0.031 mm | +0.0012" | 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 #28 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 #28 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 |
|---|---|---|---|---|
| #2 screw | 0.0860" | 0.0545" | 0.0273" | – |
| #3 screw | 0.0990" | 0.0415" | 0.0208" | – |
| #4 screw | 0.1120" | 0.0285" | 0.0143" | – |
| M3 bolt | 3 mm | 0.57 mm | 0.28 mm | Normal fit (normal 3.4, loose 3.6 mm) |
| #5 screw | 0.1250" | 0.0155" | 0.0078" | – |
| M3.5 bolt | 3.5 mm | 0.07 mm | 0.03 mm | Tighter than close fit (3.7 mm) |
| #6 screw | 0.1380" | 0.0025" | 0.0013" | – |
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 #28 drill?
A #28 drill is 0.1405 in, which is 3.57 mm (3.5687 mm exactly).
What is the metric equivalent of a #28 drill?
The nearest metric drill is 3.6 mm, 0.031 mm larger. The other close size is 3.5 mm.
What thread can I tap with a #28 drill?
It leaves about 66 % thread in M4 × 0.5 and 65 % in #8-36 UNF.
Which fractional drill is closest to #28?
9/64 in (0.1406 in) is the closest, 0.0001 in larger.
What does a #28 drill clear?
It clears a #6 screw with 0.0025" total clearance (0.0013" per side).