Lag Screw Withdrawal Design Value (NDS 12.2.1)
The lag's axial capacity from the NDS equation, not a table: W = 1,800 G^(3/2) D^(3/4) lb/in of thread penetration. A 1/2 in lag in DF-L over 4 in of thread holds 1,514 lb; step to a 5/8 in lag and it rises only 18% (the D^(3/4) law) - more or deeper lags beat one fat lag. Withdrawal (axial) value only, not the lateral yield-limit connection or the head bearing; end-grain installs take a 0.75 factor. A design aid, not the engineer of record's stamped design.
Formula and source
W = 1,800 G^(3/2) D^(3/4) (lb/in of thread); Ceg = end grain ? 0.75 : 1.0; Z_w = W x p_thread x CD x Ceg.
The NDS 2018 12.2.1 reference lag-screw withdrawal design value and the end-grain factor, by name; the 1,800 empirical constant is named.
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