Pilot hole for a 5/16" lag screw
Hardwood
13/64" to 1/4"
Softwood
9/64" to 3/16"
Published charts do not agree on lag screw pilots, so this page gives the range. Start at the smaller end and test on scrap.
5/16" lag screw pilot hole sizes
| Lag screw diameter | 5/16" 7.94 mm |
|---|---|
| Softwood, chart 1 | 9/64" |
| Softwood, chart 2 | 3/16" |
| Hardwood, chart 1 | 13/64" |
| Hardwood, chart 2 | 1/4" |
Which size to pick
The drill size depends on the wood and on the screw's thread depth. Dense wood and long screws need the larger end; soft wood the smaller.
If the screw is hard to drive or the head twists, drill a bit larger. If it spins freely, drill a bit smaller. The shank (unthreaded part) also needs its own full-diameter clearance hole in the board you are fastening.
Tools for this job
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