#8 wood screw
Diameter
0.164 in
4.17 mm · 15 threads per inch · head up to 0.332 in
From the standard, ANSI B18.6.1
Pilot hole, hardwood / softwood
7/64 or 1/8 / 3/32 in
Median of 5 sources
Holes for a #8
| Hole | Drill | Median | Charts | Nearest metric |
|---|---|---|---|---|
| Pilot, hardwood | 7/64 or 1/8 in | 0.117 in (2.98 mm) | charts span 0.094–0.125 in | 2.9 mm or 3 mm |
| Pilot, softwood | 3/32 in | 0.094 in (2.38 mm) | charts span 0.078–0.109 in | 2.3 mm or 2.4 mm |
| Clearance (top piece) | 11/64 in | 0.172 in (4.37 mm) | all charts agree | 4.3 mm or 4.4 mm |
The countersink for a flat head is 0.332 inch across (8.43 mm) and 0.191 inch deep (4.85 mm) with an 82° bit, to sit flush.
About these sizes
The diameter, threads and head size are from the ANSI B18.6.1 wood screw standard, checked against copies that agree. The holes are not standardised: each is the median of the published charts, and the span shows how far they differ. Hardwood takes the bigger pilot because, as the USDA Wood Handbook puts it, the lead hole for the threads should be about 90% of the root diameter in hardwoods and about 70% in softwoods. Drill a test hole in a scrap of the same wood when the fit matters.
Try any size and wood in the pilot hole calculator, or compare every gauge on the wood screw size chart.
Sources
- Engineers Edge, ANSI flat, pan and oval head wood screws per ANSI B18.6.1, size table; pilot hole drill sizes for wood screws, read 2026-11-07
- Engineering ToolBox, US wood screws: pilot holes, shank clearance holes and head diameters, read 2026-11-07
- Aspen Fasteners, Wood screws spec sheet: standard wood screw dimensions; 82° head angle, read 2026-11-07
- USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-190), ch. 8 Fastenings: lead holes and Table 8–9 screw shank diameters (as republished by CED Engineering, course S03-019), read 2026-11-07
- McFeely’s, Drilling chart for screw sizes (straight pilot drill, shank hole, head size), read 2026-11-07
- MISUMI USA, Wood screw pilot hole sizes chart (straight bit columns), read 2026-11-07
- Bob Vila, How to drill a pilot hole: pilot hole sizes for wood screws, read 2026-11-07
- WoodBin, Wood screw pilot holes (shank hole column), read 2026-11-07