# Flat-head wood screws, inch #4–#14 (ASME B18.6.1): body and head diameter, pilot and clearance holes from three sources + envelope models

> What drill size for a #8 wood screw pilot and clearance hole, and what are the body and head diameters?

- Category: Hardware › Fasteners
- Kind: Standard part
- Basis: AFT Fasteners and Engineers Edge for the B18.6.1 body and flat-head dimensions (they agree), three pilot-hole sources (Albany County Fasteners, Fine Power Tools, Engineers Edge) that disagree and are shown side by side; six envelope models as files
- Page: https://xemstudio.com/objects/wood-screws-flat-head-inch/ · JSON: https://xemstudio.com/api/geometry?object=wood-screws-flat-head-inch · Plain text: https://xemstudio.com/objects/wood-screws-flat-head-inch/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

## Overall (mm)

| length | width | height |
|---|---|---|
| 38.1 | 12.9 | 12.9 |

**Exact dimensions.** True size, with no tolerance added.

## Notes

- Dimensions are inches, flat (countersunk) head slotted wood screws as printed on the B18.6.1 tables: threads per inch; nominal body diameter (Engineers Edge, = 0.060 + 0.013 × the screw number) with AFT's body max / min (Engineers Edge's note gives the tolerance as +0.004 / −0.007 for cut threads); flat head diameter A max / min and head height H (ref). The two tables agree on A, H and body diameter for every size #4 to #14; the mm column is the nominal body diameter converted, computed (× 25.4). AFT's table also prints a second diameter pair per size (smaller by about 0.02 in, not labelled clearly in the text read); it is not shown.
- Pilot and clearance holes are not part of the B18.6.1 table, and the three sources disagree, so all are shown. Albany County Fasteners: softwood / hardwood pilot and clearance for #4–#14. Fine Power Tools: its first table; the page also carries a second, extended table with other values (it gives 1/16 for #4 softwood and 1/8 for #8 hardwood) that is not used. Engineers Edge: hardwood / softwood pilot only, listed there as per B18.6.1. Examples of the spread: #4 softwood pilot 5/64 (Albany) against 3/64 (Fine Power Tools and Engineers Edge); #8 softwood 7/64 against 5/64; #10 hardwood 9/64 (Albany, Fine Power Tools) against 7/64 (Engineers Edge). Clearance holes agree between Albany and Fine Power Tools for #6 to #14 (9/64, 11/64, 3/16, 7/32, 1/4) and differ for #4 (1/8 against 7/64). Pilot sizes depend on the wood and screw design: use the maker's chart for your screw.
- Files are Xem-drawn envelopes, not the real screw: the flat head is a cone from the head diameter A max (top) down to the nominal body diameter over H ref (the cone angle follows from those numbers); the body is a plain cylinder at the nominal diameter (the real thread is smaller at the root); no slot or recess, no gimlet point. The overall length 1-1/2 in (38.1 mm) is an example chosen by Xem for all six files, not a published length. The head top is flat.
- Not on this page: round, oval, pan and other heads (B18.6.1 covers them), slot and recess dimensions, thread length. Metric chipboard / wood screws 3–6 mm: no table could be verified (McMaster's metric wood-screw listings are hex-head thread-forming M6 to M16 and are lag-type screws, not this size range), so none is shown. McMaster-Carr sells wood screws with per-part STEP; its category is linked, not copied. Hex lag screws: lag-screws-hex-inch.

## Sizes

| screw # | TPI | nominal body dia (in) | nominal body dia (mm, computed) | body dia max / min (AFT, in) | flat head dia A max / min (in) | head height H ref (in) | pilot softwood / hardwood (Albany, in) | clearance (Albany, in) | pilot softwood / hardwood (Fine Power Tools, in) | clearance (Fine Power Tools, in) | pilot hardwood / softwood (Engineers Edge, in) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| #4 | 22 | .112 | 2.84 | .116 / .105 | .225 / .195 | .067 | 5/64 / 3/32 | 1/8 | 3/64 / 5/64 | 7/64 | 1/16 / 3/64 |
| #5 | 20 | .125 | 3.17 | .129 / .118 | .252 / .220 | .075 | 5/64 / 3/32 | 9/64 | — | — | — |
| #6 | 18 | .138 | 3.51 | .142 / .131 | .279 / .244 | .083 | 3/32 / 7/64 | 9/64 | 1/16 / 3/32 | 9/64 | 5/64 / 1/16 |
| #7 | 16 | .151 | 3.84 | .155 / .144 | .305 / .268 | .091 | 3/32 / 7/64 | 5/32 | — | — | — |
| #8 | 15 | .164 | 4.17 | .168 / .157 | .332 / .292 | .100 | 7/64 / 1/8 | 11/64 | 5/64 / 7/64 | 11/64 | 3/32 / 5/64 |
| #9 | 14 | .177 | 4.50 | .181 / .170 | .358 / .316 | .108 | 7/64 / 1/8 | 3/16 | — | — | — |
| #10 | 13 | .190 | 4.83 | .194 / .183 | .385 / .340 | .116 | 1/8 / 9/64 | 3/16 | 3/32 / 9/64 | 3/16 | 7/64 / 3/32 |
| #12 | 11 | .216 | 5.49 | .220 / .209 | .438 / .389 | .132 | 9/64 / 5/32 | 7/32 | 7/64 / 5/32 | 7/32 | 1/8 / 7/64 |
| #14 | 10 | .242 | 6.15 | .246 / .235 | .507 / .452 | .153 | 5/32 / 3/16 | 1/4 | 5/32 / 11/64 | 1/4 | 9/64 / 1/8 |

## Where the files are

- AFT Fasteners: [Wood screws dimensions and mechanical specs (ASME B18.6.1): nominal size, threads per inch, body diameter max / min, flat head diameter A, head height H](https://www.aftfasteners.com/wood-screws-dimensions-mechanical-specs/) — web — Publisher's page; dimensions are facts
- Engineers Edge: [ANSI B18.6.1 wood screw dimensions: threads per inch, body diameter, flat head diameter A max / min, head height H](https://ns2.engineersedge.com/hardware/ansi_wood_screws_per_ansi_b1861__14855.htm) — web — Publisher's page; dimensions are facts
- Albany County Fasteners: [Wood screw pilot hole guide: softwood pilot, hardwood pilot, clearance hole by screw size #2 to 5/16](https://www.albanycountyfasteners.com/media/51/31/8c/1764682594/wood-screw-pilot-hole-guide.pdf) — web — Distributor guide; numbers only
- Fine Power Tools: [What size drill bit for a screw: softwood pilot, hardwood pilot, shank clearance hole #4 to #14](https://www.finepowertools.com/woodworking/what-size-drill-bit-for-screw/) — web — Tool-review page; numbers only (its second table has other values)
- Engineers Edge: [Pilot hole drill sizes for wood screws, hardwood and softwood, #2 to #14 (page says per ANSI B18.6.1)](https://engineersedge.com/hardware/pilot_hole_drill_sizes_wood_screws_14857.htm) — web — Publisher's page; dimensions are facts
- McMaster-Carr: [Wood screws (free STEP/IGES per part, for your own design use; no redistribution)](https://www.mcmaster.com/wood-screws) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution (verify at link)

## Free STEP/STL (6 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/index.json

- wood-screw-no4-flat-head-1-1-2in-envelope: [STEP](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no4-flat-head-1-1-2in-envelope.step) · [STL](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no4-flat-head-1-1-2in-envelope.stl) — #4 flat-head wood screw envelope: head Ø5.71 mm (A max .225 in) tapering to the Ø2.845 mm nominal body over 1.70 mm (H ref .067 in); plain body, example overall length 1-1/2 in (38.1 mm, Xem's choice); no thread, slot, recess or point
- wood-screw-no6-flat-head-1-1-2in-envelope: [STEP](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no6-flat-head-1-1-2in-envelope.step) · [STL](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no6-flat-head-1-1-2in-envelope.stl) — #6 flat-head wood screw envelope: head Ø7.09 mm (A max .279 in) tapering to the Ø3.505 mm nominal body over 2.11 mm (H ref .083 in); plain body, example overall length 1-1/2 in (38.1 mm, Xem's choice); no thread, slot, recess or point
- wood-screw-no8-flat-head-1-1-2in-envelope: [STEP](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no8-flat-head-1-1-2in-envelope.step) · [STL](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no8-flat-head-1-1-2in-envelope.stl) — #8 flat-head wood screw envelope: head Ø8.43 mm (A max .332 in) tapering to the Ø4.166 mm nominal body over 2.54 mm (H ref .100 in); plain body, example overall length 1-1/2 in (38.1 mm, Xem's choice); no thread, slot, recess or point
- wood-screw-no10-flat-head-1-1-2in-envelope: [STEP](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no10-flat-head-1-1-2in-envelope.step) · [STL](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no10-flat-head-1-1-2in-envelope.stl) — #10 flat-head wood screw envelope: head Ø9.78 mm (A max .385 in) tapering to the Ø4.826 mm nominal body over 2.95 mm (H ref .116 in); plain body, example overall length 1-1/2 in (38.1 mm, Xem's choice); no thread, slot, recess or point
- wood-screw-no12-flat-head-1-1-2in-envelope: [STEP](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no12-flat-head-1-1-2in-envelope.step) · [STL](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no12-flat-head-1-1-2in-envelope.stl) — #12 flat-head wood screw envelope: head Ø11.13 mm (A max .438 in) tapering to the Ø5.486 mm nominal body over 3.35 mm (H ref .132 in); plain body, example overall length 1-1/2 in (38.1 mm, Xem's choice); no thread, slot, recess or point
- wood-screw-no14-flat-head-1-1-2in-envelope: [STEP](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no14-flat-head-1-1-2in-envelope.step) · [STL](https://xemstudio.com/files/hardware/wood-screws-flat-head-inch/wood-screw-no14-flat-head-1-1-2in-envelope.stl) — #14 flat-head wood screw envelope: head Ø12.88 mm (A max .507 in) tapering to the Ø6.147 mm nominal body over 3.89 mm (H ref .153 in); plain body, example overall length 1-1/2 in (38.1 mm, Xem's choice); no thread, slot, recess or point

## Questions

**What is the head diameter of a #8 flat-head wood screw?**

0.332 in max and 0.292 in min (A) in both AFT's and Engineers Edge's B18.6.1 tables; head height H 0.100 in (ref).

**What clearance hole for a #8 wood screw?**

11/64 in in both Albany County Fasteners' and Fine Power Tools' tables.

**What pilot hole for a #8 wood screw?**

The sources disagree. Softwood: 7/64 (Albany), 5/64 (Fine Power Tools), 5/64 (Engineers Edge). Hardwood: 1/8 (Albany), 7/64 (Fine Power Tools), 3/32 (Engineers Edge). Check the screw maker's chart.

## Fits with

- [Hex lag screws, 1/4 to 1/2 in (ASME B18.2.1): shank, head width and height, pilot holes + envelope models](https://xemstudio.com/objects/lag-screws-hex-inch/)
- [Countersunk socket screws, M2–M8 (ISO 10642 / DIN 7991)](https://xemstudio.com/objects/countersunk-screws-metric/)
- [Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20](https://xemstudio.com/objects/imperial-machine-screws/)
- [Hex bolts, inch: 1/4-20 to 3/4-10 (ASME B18.2.1)](https://xemstudio.com/objects/hex-bolts-inch/)
- [Socket head cap screws, inch: #10-24, #10-32, 5/16-18, 3/8-16, 1/2-13 (ASME B18.3)](https://xemstudio.com/objects/socket-head-cap-screws-inch/)