Clearance hole chart
Recommended clearance hole sizes for bolts and screws in close, normal, and loose fits. Drill the through-hole in the top part to one of these sizes so the fastener passes freely while the parts still align.
Inch bolts (drill diameter, in)
| Bolt size | Close fit | Normal fit | Loose fit |
|---|---|---|---|
| #6 | 0.144 (#27) | 0.150 (#25) | 0.157 (#22) |
| #8 | 0.169 (#18) | 0.177 (#16) | 0.185 (#13) |
| #10 | 0.196 (#9) | 0.201 (#7) | 0.209 (#4) |
| 1/4 | 0.266 (17/64) | 0.281 (9/32) | 0.297 (19/64) |
| 5/16 | 0.328 (21/64) | 0.344 (11/32) | 0.359 (23/64) |
| 3/8 | 0.391 (25/64) | 0.406 (13/32) | 0.422 (27/64) |
| 1/2 | 0.516 (33/64) | 0.531 (17/32) | 0.547 (35/64) |
| 5/8 | 0.641 (41/64) | 0.656 (21/32) | 0.672 (43/64) |
Metric bolts (drill diameter, mm)
| Bolt size | Close fit | Normal fit | Loose fit |
|---|---|---|---|
| M3 | 3.2 | 3.4 | 3.6 |
| M4 | 4.3 | 4.5 | 4.8 |
| M5 | 5.3 | 5.5 | 5.8 |
| M6 | 6.4 | 6.6 | 7.0 |
| M8 | 8.4 | 9.0 | 10.0 |
| M10 | 10.5 | 11.0 | 12.0 |
| M12 | 13.0 | 13.5 | 14.5 |
| M16 | 17.0 | 17.5 | 18.5 |
Clearance holes go in the part the fastener passes through, not the part it threads into. A close fit keeps parts precisely located; a normal fit suits general assembly; a loose fit allows for misalignment and tolerance stack-up. Values follow common ASME and ISO clearance-hole standards.
Drilling the tapped hole instead?
For the threaded hole rather than the clearance hole, the Tap Drill Calculator gives the correct tap drill size.
Clearance hole vs tapped hole
A bolted joint usually has two holes: a clearance hole in the top part that the bolt passes through, and a tapped hole or nut on the other side that the bolt threads into. This chart sizes the clearance hole; the tapped hole uses a smaller tap drill.
Choosing close, normal, or loose
Close fits locate parts accurately but leave little room for error. Normal fits are the everyday choice. Loose fits give the most room for misalignment and thermal movement, useful for long bolt patterns. Oversized holes often need a washer to spread the load.
FAQ
What size clearance hole for a 1/4 inch bolt?
About 0.281 in (a 9/32 drill) for a normal fit. Use 0.266 in for a close fit or 0.297 in for a loose fit.
What is the difference between a clearance hole and a tap drill?
A clearance hole is larger than the bolt so it passes through freely; a tap drill is smaller so threads can be cut into it. They are on opposite sides of the joint.
Do I need a washer with a clearance hole?
Often yes, especially with loose fits or soft materials. A washer spreads the clamp load and bridges an oversized hole.