Use a No. 36 drill for a 6-32 cutting tap
A 6-32 cutting tap uses a No. 36 drill (0.1065 in). Compare metric and fractional substitutes, forming-tap holes and screw-clearance sizes.
Use a No. 36 drill bit for a conventional 6-32 cutting tap. A No. 36 bit measures 0.1065 inch (2.705 mm), the chart size listed for 6-32 threads by American Fastener Technologies.
Do not use that answer automatically for a thread-forming tap or for a hole the screw must pass through. Those operations require larger holes.
| Hole purpose | Drill size | Diameter |
|---|---|---|
| 6-32 cutting tap | No. 36 | 0.1065 in / 2.705 mm |
| Close metric substitute for cutting tap | 2.7 mm | 0.1063 in |
| Fractional substitute for cutting tap | 7/64 in | 0.1094 in / 2.778 mm |
| 6-32 forming or roll tap starting point | 3.1 mm | 0.1221 in |
| Close-fit screw clearance | No. 27 | 0.144 in |
| Free-fit screw clearance | No. 25 | 0.1495 in |
Choose the hole by its purpose
A 6-32 screw has a nominal major diameter of 0.138 inch and 32 threads per inch. The University of Florida’s tap and clearance chart lists No. 36 for a typical 6-32 tapped hole, plus No. 27 and No. 25 for close- and free-fit #6 clearance holes.
The 2.7 mm substitute is only about 0.0002 inch smaller than No. 36, making it the closest straightforward metric choice.
A 7/64-inch bit is 0.0029 inch larger than No. 36. It is a practical fractional substitute when a numbered bit is unavailable, but the larger pilot leaves less material for the tap to cut. Prefer No. 36 or 2.7 mm when thread engagement matters. Do not substitute 3/32 inch: at 0.09375 inch, it is substantially undersized and will increase tapping torque and the risk of breaking this small tap.
A forming tap displaces material instead of cutting it, so it needs a larger starting hole. Haas lists 3.1 mm (0.1221 inch) for a 6-32 roll tap, corresponding to about 75% thread in that chart. Haas also calls its recommendation a starting point because material, hardness and tolerance can change the required hole size; follow the exact tap manufacturer’s data when available. See the Haas roll-tap drill chart.
Drill and tap the hole
- Confirm that the tap is marked 6-32 and determine whether it is a cutting or forming tap.
- Clamp the work securely, wear eye protection and drill perpendicular to the surface with the selected bit.
- For a blind hole, allow extra depth beyond the required full threads for the tap’s chamfer and, with a cutting tap, chip space. Check what is behind the work before drilling.
- Lightly chamfer or deburr the entrance so the tap can start cleanly.
- Apply a cutting fluid suitable for the workpiece, align the tap squarely and turn it without side loading. When hand tapping with a conventional straight-flute cutting tap, periodically reverse as needed to break chips; other tap styles may require a different method.
- Stop if torque rises sharply. Back the tap out, clear chips and check alignment rather than forcing it.
- Clean the finished thread and verify it with the intended 6-32 screw or the specified thread gage.
For nearby machine-screw sizes, the pilot changes: an 8-32 cutting tap takes No. 29, covered in the 8-32 tap-drill guide, while the 10-32 tap-drill guide uses No. 21.