Wood Screw Dimensions

Boring Chart for Wood Screws How to use this chart: The table of wood screw specifications simplifies the selection of the bit or drill size best suited to your rquirements. The fractional equivalents and undersize or oversize decimals indicate how close a bit of given fractional size will bore to the actual screw dimension and whether the fit will be snug or loose. In selecting a tool size for the pilot hole (for the threaded portion of the screw), note that root diameters are average dimensions measured at the middle of the threaded portion. On some screws the root diameter tapers slightly from the end to the smooth shank. It is usually good practice to bore the pilot hole the same size as the root diameter in hardwoods, and about 15% smaller in softwoods. The SHANK DIAMETERS shown below are standard specifications subject to tolerances of plus 0.004" and minus 0.007". MAXIMUM HEAD DIAMETERS are also standard specifications which apply to flathead and ovalhead screws. Head sizes run 5% to 10% smaller in roundhead screws. Number of THREADS PER INCH is rounded to the nearest whole number; this is especially noticeable in the larger sizes. #   Shank Diameter Root Diameter    #  of Screw  Max. Head Dia. Basic Dec. Size Nearest Fractional Equivalent Avg. Dec. Size Nearest Fractional Equivalent Threads Per Inch of Screw 0 .119 .060 1/16 Oversize .002 .040 3/64 Oversize .007 32 0 1 .146 .073 5/64 Oversize .005 .048 3/64 Basic Size 28 1 2 .172 .086 3/32 Oversize .007 .054 1/16 Oversize .008 26 2 3 .199 .099 7/64 Oversize .010 .065 1/16 Undersize .002 24 3 4 .225 .112 7/64 Undersize .003 .075 5/64 Oversize .003 22 4 5 .252 .125 1/8 Basic Size .085 5/64 Undersize .007 20 5 6 .279 .138 9/64 Oversize .002 .094 3/32 Basic Size 18 6 7 .305 .151 5/32 Oversize .005 .102 7/64 Oversize .007 16 7 8 .332 .164 5/32 Undersize .007 .112 7/64 Undersize .003 15 8 9 .358 .177 11/64 Undersize .005 .122 1/8 Oversize .003 14 9 10 .385 .190 3/16 Undersize .002 .130 1/8 Undersize .005 12 10 11 .411 .203 13/64 Basic Size .139 9/64 Oversize .001 12 11 12 .438 .216 7/32 Oversize .003 .148 9/64 Undersize .007 11 12 14 .491 .242 1/4 Oversize .008 .165 5/32 Undersize .009 10 14 16 .544 .268 17/64 Undersize .002 .184 3/16 Oversize .003 9 16 18 .597 .294 19/64 Oversize .003 .204 13/64 Undersize .001 8 18 20 .650 .320 5/16 Undersize .007 .223 7/32 Undersize .004 8 20 22 .680 .348 11/32 Undersize .004  .241 15/64 Undersize .007 7 22 24 .756 .372 3/8 Oversize .003 .260 1/4 Undersize .004 7 24 28 .835 .422 27/64 Undersize .001 .280 9/32 Oversize .001 6 28

Countersink Chart

Use Type "C" (Carbon Steel) Countersinks, with your taper-point, brad-point, or regular-point drill bits, to drill countersunk pilot holes for your wood screws. Type "C" Countersinks, for pre-drilling in wood Stock Number Cutting Diameter Pilot Drill Size Overall Length   Stock Number Cutting Diameter Pilot Drill Size Overall Length                             C122 1/2 1/8 7/8           C129 1/2 9/64 7/8 C2 1/4 5/64 3/4   C125 1/2 5/32 7/8 C3 1/4 3/32 3/4   C1211 1/2 11/64 7/8           C92 1/2 3/16 7/8           C102 1/2 13/64 7/8 C4 5/16 7/64 7/8   C12 1/2 7/32 7/8 C44 5/16 1/8 7/8   C1415 1/2 15/64 7/8 C65 5/16 9/64 7/8   C14 1/2 1/4 7/8 C410 5/16 5/32 7/8           C411 5/16 11/64 7/8   C145 5/8 5/32 1-1/16 C43 5/16 3/16 7/8   C143 5/8 3/16 1-1/16           C167 5/8 7/32 1-1/16           C16 5/8 1/4 1-1/16 C56 3/8 3/32 7/8   C1617 5/8 17/64 1-1/16 C57 3/8 7/64 7/8   C169 5/8 9/32 1-1/16 C5 3/8 1/8 7/8   C1619 5/8 19/64 1-1/16 C6 3/8 9/64 7/8   C18 5/8 5/16 1-1/16 C7 3/8 5/31 7/8           C8 3/8 11/64 7/8   C243 3/4 3/16 1-1/8 C9 3/8 3/16 7/8   C247 3/4 7/32 1-1/8 C913 3/8 13/64 7/8   C244 3/4 1/4 1-1/8 C97 3/8 7/32 7/8   C245 3/4 5/16 1-1/8           C20 3/4 21/64 1-1/8           C24 3/4 3/8 1-1/8 C105 7/16 5/32 7/8           C1011 7/16 11/64 7/8   C284 7/8  1/4 1-1/4 C103 7/16 3/16 7/8   C285 7/8 5/16 1-1/4 C10 7/16 13/64 7/8   C286 7/8 3/8 1-1/4 C1014 7/16 7/32 7/8   C287 7/8 7/16 1-3/8 C104 7/16 1/4 7/8                     C324 1" 1/4 1-3/8           C326 1" 3/8 1-3/8           C328 1"  1/2 1-1/2