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Wood Screws - Withdrawal Force

Allowable withdrawal load force.

Allowable withdrawal load or force of a common wood screw into side grain perpendicular to the fibers of seasoned dry wood can be expressed as

F = 2850 SG2D                   (1)


F = allowable withdrawal load or force - lb per inch of penetration (lb/in)

SG = specific gravity of oven dry wood

D = diameter of screw (in)

Wood screws - shank diameters and pitot holes

Note the difference between allowable load and failure load. Allowable load includes design and safety factors and ranges typically between 2 and 10. Depending on the case allowable load is normally 10 - 50% of the failure load.

Example - Screw Allowable Withdrawal Load

The specific gravity of Canadian Spruce is 0.45 . The diameter of no. 10 screw is 0.190 inches . The withdrawal force per inch of penetration can be estimated as

F = 2850 (0.45)2(0.190 in)

= 109 lb per inch of penetration

Screw Withdrawal Force Calculator

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