Threaded nails are used in wood construction because of their superior performance, but relatively few tests have been conducted on nails larger than 12d (3.76 mm diameter). Experience has suggested that threaded nail withdrawal design values are too conservative. The Forest Products Laboratory and Washington State University have been cooperatively characterizing the strength of threaded nails over a range of wood species and nail types. This paper focuses on the immediate withdrawal strength of annularly threaded nails in Douglas Fir and Spruce-Pine-Fir, helically threaded nails in Southern Pine, and smooth nails in Southern Pine and Spruce-Pine-Fir lumber. Average withdrawal strength of threaded nails was greater than that of smooth shank nails of the same diameter. In comparison of experimental withdrawal strength to existing design proce- dures for assigning allowable withdrawal strength design values, annular shank nails showed the greatest dif- ference. Withdrawal strengths of nails from five different manufacturers were not significantly different. Com- parisons of the effect of galvanizing on withdrawal strength were inconclusive.
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