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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? · 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

Also called: wood screw pilot hole size, #8 wood screw pilot hole, #10 wood screw drill bit, #6 wood screw clearance hole, wood screw head diameter, #8 flat head wood screw head diameter, wood screw size chart, #10 wood screw diameter, b18.6.1 wood screw dimensions, #8 screw pilot hole softwood hardwood, #12 wood screw dimensions

Exact dimensions. True size, with no tolerance added.

length
38.1 mm
width
12.9 mm
height
12.9 mm

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.

Flat-head wood screws, inch #4–#14 (ASME B18.6.1): body and head… size chart

screw #TPInominal 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)
#422.1122.84.116 / .105.225 / .195.0675/64 / 3/321/83/64 / 5/647/641/16 / 3/64
#520.1253.17.129 / .118.252 / .220.0755/64 / 3/329/64———
#618.1383.51.142 / .131.279 / .244.0833/32 / 7/649/641/16 / 3/329/645/64 / 1/16
#716.1513.84.155 / .144.305 / .268.0913/32 / 7/645/32———
#815.1644.17.168 / .157.332 / .292.1007/64 / 1/811/645/64 / 7/6411/643/32 / 5/64
#914.1774.50.181 / .170.358 / .316.1087/64 / 1/83/16———
#1013.1904.83.194 / .183.385 / .340.1161/8 / 9/643/163/32 / 9/643/167/64 / 3/32
#1211.2165.49.220 / .209.438 / .389.1329/64 / 5/327/327/64 / 5/327/321/8 / 7/64
#1410.2426.15.246 / .235.507 / .452.1535/32 / 3/161/45/32 / 11/641/49/64 / 1/8

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

AFT FastenersWood screws dimensions and mechanical specs (ASME B18.6.1): nominal size, threads per inch, body diameter max / min, flat head diameter A, head height HwebPublisher's page; dimensions are facts
Engineers EdgeANSI B18.6.1 wood screw dimensions: threads per inch, body diameter, flat head diameter A max / min, head height HwebPublisher's page; dimensions are facts
Albany County FastenersWood screw pilot hole guide: softwood pilot, hardwood pilot, clearance hole by screw size #2 to 5/16webDistributor guide; numbers only
Fine Power ToolsWhat size drill bit for a screw: softwood pilot, hardwood pilot, shank clearance hole #4 to #14webTool-review page; numbers only (its second table has other values)
Engineers EdgePilot hole drill sizes for wood screws, hardwood and softwood, #2 to #14 (page says per ANSI B18.6.1)webPublisher's page; dimensions are facts
McMaster-CarrWood screws (free STEP/IGES per part, for your own design use; no redistribution)STEP, IGES, PDFMcMaster-Carr site terms: personal design use, no redistribution verify

Free files

★ Free files 6 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json

wood-screw-no4-flat-head-1-1-2in-envelope#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 pointSTEP · STL
wood-screw-no6-flat-head-1-1-2in-envelope#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 pointSTEP · STL
wood-screw-no8-flat-head-1-1-2in-envelope#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 pointSTEP · STL
wood-screw-no10-flat-head-1-1-2in-envelope#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 pointSTEP · STL
wood-screw-no12-flat-head-1-1-2in-envelope#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 pointSTEP · STL
wood-screw-no14-flat-head-1-1-2in-envelope#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 pointSTEP · STL
Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.
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Plain text: sheet.txt · JSON: /api/geometry?object=wood-screws-flat-head-inch

Flat-head wood screws, inch #4–#14 (ASME B18.6.1): body and head diameter, pilot and clearance holes from three sources + envelope models, isometric render of a generated part
Render of wood-screw-no10-flat-head-1-1-2in-envelope from the free STEP; not to scale.

Fits with

Hex lag screws, 1/4 to 1/2 in (ASME B18.2.1): shank, head width and height, pilot holes + envelope models, isometric render of a generated part
Hex lag screws, 1/4 to 1/2 in (ASME B18.2.1): shank, head width and height, pilot holes + envelope models22.0×19.0×84.9 mm★ 5 files
Countersunk socket screws, M2–M8 (ISO 10642 / DIN 7991), isometric render of a generated part
Countersunk socket screws, M2–M8 (ISO 10642 / DIN 7991)7 sizes★ 35 files
Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20, isometric render of a generated part
Imperial machine screws: #4-40, #6-32, #8-32, 1/4-204 sizes★ 18 files
Hex bolts, inch: 1/4-20 to 3/4-10 (ASME B18.2.1), isometric render of a generated part
Hex bolts, inch: 1/4-20 to 3/4-10 (ASME B18.2.1)7 sizes★ 47 files
Socket head cap screws, inch: #10-24, #10-32, 5/16-18, 3/8-16, 1/2-13 (ASME B18.3), isometric render of a generated part
Socket head cap screws, inch: #10-24, #10-32, 5/16-18, 3/8-16, 1/2-13 (ASME B18.3)5 sizes★ 25 files

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.