The specifications state that the wall construction must be able to take a pullout load of 1.4 KN or 140 kp. Pull-out strength and shear strength values are 25% of the ultimate values. The lead hole for the shank should be the same diameter as the shank. Besides, a lag screw's pull-out capacity is strongest with southern pine, at 307 pounds. Engineering Book Store In practice, a lag screw's ability to resist "pull out" or withdrawal sideration [ 2]. A single 1/4" Grade 5 lag bolt, in a configuration like this, will fail at roughly 13,000 lbs. { DFM DFA Training A 5/16" dia. A lag screw's head and washer must be screwed flush to the surface but not overtightened, as overtightening breaks the wood fibers underneath. The following equations for withdrawal and lateral loads are based on lag screws having a base metal average tensile yield strength of about 310.3 MPa (45,000 lb/in2) and an average ultimate tensile strength of 530.9 MPa (77,000 lb/in2).