A clearance hole is the hole a bolt slides through — in a bracket, a flange, a plate — before it threads into something or takes a nut. Make it a touch bigger than the bolt so the bolt isn’t fighting the hole. How much bigger depends on the fit you need: close for precise alignment, normal for everyday assembly, loose when there’s a coating, slop, or field misalignment to swallow.
Tightest hole — for precise location with little play.
The everyday choice for general bolt-up.
Most room — for galvanized bolts, field work, or easy assembly.
| Bolt size | Close fit | Normal fit | Loose fit |
|---|---|---|---|
| #8 | 0.180″ | 0.196″ | 0.213″ |
| #10 | 0.206″ | 0.221″ | 0.238″ |
| ¼″ | 0.266″ | 0.281″ | 0.297″ |
| 5⁄16″ | 0.328″ | 0.344″ | 0.359″ |
| ⅜″ | 0.391″ | 0.406″ | 0.422″ |
| 7⁄16″ | 0.453″ | 0.469″ | 0.484″ |
| ½″ | 0.531″ | 0.562″ | 0.609″ |
| 5⁄8″ | 0.656″ | 0.688″ | 0.734″ |
| ¾″ | 0.781″ | 0.812″ | 0.906″ |
| 7⁄8″ | 0.906″ | 0.938″ | 1.031″ |
| 1″ | 1.031″ | 1.094″ | 1.156″ |
They’re opposite jobs. A clearance hole (this chart) is bigger than the bolt, so the bolt passes through. A tap drill is smaller than the bolt, so threads can be cut into the hole. If you’re cutting threads, you want the tap-drill chart instead.
Going through galvanized or coated parts? Lean to the loose column — the coating eats into the clearance. And for slotted or oversized structural holes, the connection design sets the size; ask if you’re unsure.
