Wood screw · ASME B18.6.1
#8wood
0.164" / 4.17 mm shank
Wood screw
- Shank diameter
- 0.164" · 4.17 mmnearest 5/32"
- Countersink diameter
- 0.332" · 8.43 mm
Drill bits
- Pilot · hardwood
- 3/32"
- Pilot · softwood
- 5/64"
- Shank clearance
- 11/64"
Wood screw & pocket-hole size chart
Gauge #0 to #16 with hardwood and softwood pilot holes, shank clearance, countersink and a pocket-hole screw guide.
Full chart 24 rows
Sort any column, filter by series, print a shop sheet. Click a row to load it on the gauge.
Wood screw size chart
17 rowsWood screw size chart · ScrewBoltChart
screwboltchart.com · inch-first · tap drills 75% (soft metals) · torque dry, K=0.20 · verify against the governing standard
| 0.060" · 1.52 mm | 1/16" | 1/32" | 1/64" | 1/16" | 0.119" | ||
| 0.073" · 1.85 mm | 5/64" | 1/32" | 1/32" | 5/64" | 0.146" | ||
| 0.086" · 2.18 mm | 3/32" | 3/64" | 1/32" | 3/32" | 0.172" | ||
| 0.099" · 2.51 mm | 3/32" | 1/16" | 3/64" | 7/64" | 0.199" | ||
| 0.112" · 2.84 mm | 7/64" | 1/16" | 3/64" | 7/64" | 0.225" | ||
| 0.125" · 3.18 mm | 1/8" | 5/64" | 1/16" | 1/8" | 0.252" | ||
| 0.138" · 3.51 mm | 9/64" | 5/64" | 1/16" | 9/64" | 0.279" | ||
| 0.151" · 3.84 mm | 5/32" | 3/32" | 1/16" | 5/32" | 0.305" | ||
| 0.164" · 4.17 mm | 5/32" | 3/32" | 5/64" | 11/64" | 0.332" | ||
| 0.177" · 4.5 mm | 11/64" | 7/64" | 5/64" | 3/16" | 0.358" | ||
| 0.190" · 4.83 mm | 3/16" | 7/64" | 3/32" | 3/16" | 0.385" | ||
| 0.203" · 5.16 mm | 13/64" | 1/8" | 3/32" | 13/64" | 0.411" | ||
| 0.216" · 5.49 mm | 7/32" | 1/8" | 7/64" | 7/32" | 0.438" | ||
| 0.229" · 5.82 mm | 15/64" | 9/64" | 7/64" | 15/64" | 0.464" | ||
| 0.242" · 6.15 mm | 15/64" | 9/64" | 7/64" | 1/4" | 0.491" | ||
| 0.255" · 6.48 mm | 1/4" | 5/32" | 1/8" | 17/64" | 0.517" | ||
| 0.268" · 6.81 mm | 17/64" | 5/32" | 9/64" | 17/64" | 0.544" |
Pocket-hole screw guide (Kreg-style jigs)
7 rowsPocket-hole screw guide (Kreg-style jigs) · ScrewBoltChart
screwboltchart.com · inch-first · tap drills 75% (soft metals) · torque dry, K=0.20 · verify against the governing standard
| 1/2" | 1" | Coarse thread | Fine thread | 1/2" setting |
| 5/8" | 1" | Coarse thread | Fine thread | 5/8" setting |
| 3/4" | 1-1/4" | Coarse thread | Fine thread | 3/4" setting |
| 7/8" | 1-1/2" | Coarse thread | Fine thread | 7/8" setting |
| 1" | 1-1/2" | Coarse thread | Fine thread | 1" setting |
| 1-1/4" | 2" | Coarse thread | Fine thread | 1-1/4" setting |
| 1-1/2" | 2-1/2" | Coarse thread | Fine thread | 1-1/2" setting |
05 / Field guide
Pilot holes
that hold.
A wood screw grips by displacing fibres. Too small a pilot and hardwood splits or the screw snaps; too large and it strips. The right pilot depends on the gauge, the wood and whether the screw passes through the first board.
Three holes for one screw
The pilot hole in the bottom board is roughly the screw’s root diameter: smaller in softwood, closer to the root in hardwood. The shank clearance hole in the top board lets the screw pull the boards together instead of jacking them apart. The countersink lets a flat head sit flush.
Hardwood or softwood
Softwoods (pine, fir, cedar) compress around the thread, so a smaller pilot gives the best hold. Hardwoods (oak, maple, ash) don’t give, so they need a larger pilot to avoid splitting and snapped screws. Modern self-drilling screws need smaller pilots than the traditional tapered screws this chart is based on, so when in doubt, test in scrap.
Pocket-hole screws
Pocket-hole joints use a stepped drill and a jig set to the stock thickness. Use coarse-thread screws in softwood, plywood and MDF, and fine-thread screws in hardwood. For 3/4" stock use 1-1/4" screws, and set both the drill collar and the jig to 3/4".
Countersinking flat heads
A flat-head wood screw has an 82° head, while most countersink bits sold for wood are 82° too. Drill the countersink until its diameter at the surface matches the head: about 0.33" for a #8 and 0.39" for a #10. In softwood the head can pull itself in; in hardwood it will split the surface or stand proud unless you countersink first. Combination pilot-countersink bits do all three holes in one pass.
Screw length
As a rule, at least half the screw, and ideally two-thirds, should be in the bottom board. For two 3/4" boards a 1-1/4" screw leaves 1/2" in the bottom piece; a 1-1/2" screw holds better without breaking through.
Questions
Answered plainly.
01What size pilot hole for a #8 wood screw?+−
About 3/32" in hardwood and 5/64" in softwood, with an 11/64" clearance hole through the top board. With modern coated construction screws you can often skip the pilot in softwood.
02What drill bit for a #10 wood screw?+−
A 7/64" pilot in hardwood, 3/32" in softwood and a 3/16" shank clearance hole.
03How big is a #8 wood screw?+−
A #8 wood screw has a 0.164" (4.17 mm) shank, the same nominal diameter as a #8 machine screw. The flat head is about 0.332" across.
04What length pocket-hole screw for 3/4" plywood?+−
1-1/4" coarse-thread screws, with the drill collar and jig set to 3/4". For 1-1/2" stock use 2-1/2" screws.
05When do I need a clearance hole?+−
Whenever you are joining two boards. Without one, the threads bite into both boards and hold them apart. Drill the clearance hole through the top board only, at the shank diameter or slightly larger.
06Why do screws split hardwood near the end?+−
End grain and edges have little material to resist the wedge of the screw. Use the full hardwood pilot size, keep at least 3/4" from the end, and drill a clearance hole in the top board.
07Do I need a pilot hole in softwood?+−
For small screws in pine away from the edges, often not. Near ends and edges, for gauge #10 and up, or with brass and other soft screws, drill one anyway to avoid splitting and snapped heads.
08Coarse or fine pocket-hole screws in plywood?+−
Coarse. Plywood, MDF and particleboard need the deeper, wider thread to grip. Fine-thread pocket screws are for dense hardwoods like oak and maple.
09What pilot hole for a #6 wood screw?+−
About 5/64" in hardwood and 1/16" in softwood, with a 9/64" shank clearance hole.