Pilot Hole
3/32"
Exact
0.098"
Metric
2.5mm
Screw: #8 (hardwood)
Method: Pilot = root diameter (100%)
Root dia: 0.098" | Major dia: 0.164"
Inputs
Result
Root diameter 0.098" rounds to 7/64" drill bit
Inputs
Result
85% of root diameter 0.112" = 0.095" rounds to 3/32"
For hardwood, the pilot hole should equal the screw root diameter. For softwood, use 85% of the root diameter. A #8 screw needs a 7/64" bit in hardwood or a 5/64" bit in softwood.
| Screw | Hardwood | Softwood | Clearance |
|---|---|---|---|
| #6 | 5/64" | 1/16" | 9/64" |
| #8 | 7/64" | 5/64" | 11/64" |
| #10 | 7/64" | 3/32" | 13/64" |
| #12 | 1/8" | 7/64" | 7/32" |
Always in hardwood to prevent splitting. In softwood, pilot holes are recommended near edges, in thin stock, and with larger screws (#10+). Without a pilot hole, screws can split the wood and fail to seat properly.
A pilot hole is drilled in the receiving piece and is smaller than the screw to allow threads to grip. A clearance hole is drilled in the top piece and is larger than the screw so it passes through freely, pulling the joint tight.
Drill the pilot hole at least as deep as the screw will penetrate. For most wood screws, this is the full screw length minus the top board thickness. Use masking tape on the drill bit as a depth stop.
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Last Updated: Mar 20, 2026
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