Find a screw size and its drill bit
Type a size such as #8, 1/4-20 or M6 and get the diameter, thread, tap drill, pilot hole and clearance hole, with the assumption stated.
Common sizes
| Size | Type | Diameter | Thread | Tap drill |
|---|---|---|---|---|
| #6 | Machine (inch) | 0.1380 in | 32 TPI | #36 |
| #8 | Machine (inch) | 0.1640 in | 32 TPI | #29 |
| #10 | Machine (inch) | 0.1900 in | 24 TPI | #25 |
| 1/4 | Machine (inch) | 0.2500 in | 20 TPI | #7 |
| M4 | Metric | 4.0 mm | 0.7 mm pitch | 3.30 mm |
| M5 | Metric | 5.0 mm | 0.8 mm pitch | 4.20 mm |
| M6 | Metric | 6.0 mm | 1.0 mm pitch | 5.00 mm |
| M8 | Metric | 8.0 mm | 1.25 mm pitch | 6.80 mm |
A #8 machine screw is 0.1640 in across and takes a #29 tap drill for its 32 TPI coarse thread. For the full lists see the screw size chart, or go straight to the drill bit finder.
How to use the lookup
Type a size as printed on the packet or the screw head: #8, #8-32, 1/4-20, M6 or M8 x 1. A bare number such as #8 is read as a machine screw unless you switch the type to wood screw. Add a thread count (the 32 in #8-32) or a pitch (the 1 in M8 x 1) to pick one thread series; leave it off and the standard coarse thread comes first.
Which kind of screw do I have?
Machine screws have a uniform thread and go into a nut or a tapped hole. Wood screws have a tapered tip and a coarse thread that cuts its own path into wood. Metric screws are labelled with an M and a diameter in millimetres; inch screws use a gauge number (#4, #8, #10) or a fraction of an inch. A #8 machine screw and a #8 wood screw share a nominal diameter of 0.164 in but need different holes, so the three families are kept apart.
What the results mean
The tap drill is the hole you drill before cutting threads with a tap. The clearance hole is the hole a screw passes through freely, in the top plate of an assembly. The pilot hole is the guide hole you drill before driving a wood screw. Every result names the source or the assumption behind it.