5/16 Tap Drill Size and Drill Bit for a 5/16
Use a F drill bit
5/16 · 0.257 in / 6.53 mm · ~75% thread
A 5/16 tap is usually the 5/16-18 coarse UNC thread. A letter F bit is the correct tap drill for a strong 75% thread.
At a glance
| Tap drill | F |
|---|---|
| Inches | 0.257 in |
| Millimetres | 6.53 mm |
| Major diameter | 0.3125 in |
| Pitch | 0.0556 in |
| Threads per inch | 18 |
Why this size
drillØ = major − (pitch × %thread) = 0.3125 − (0.0556 × 0.75) = 0.2708 in → next standard drill F (0.257 in / 6.53 mm)
A 5/16-24 fine version uses a letter I bit. This reference covers the standard 5/16-18 coarse thread.
Clearance holes for 5/16
A clearance hole lets the bolt pass through unthreaded – close fit keeps parts aligned, free fit allows movement.
| Tap drill (cuts threads) | F |
|---|---|
| Close fit clearance | 21/64 bit |
| Free fit clearance | 23/64 bit |
Related sizes
Compare with adjacent threads – coarse, fine and the opposite measurement system:
All 5/16 thread sizes
The 5/16 diameter comes in both coarse and fine pitch. Each has its own tap drill: