High-grade alloy steel bolt of Model L°9 is heat treated to reach 180,000 psi minimum tensile strength. Thick bolt head adds wrenching surface. Countersunk washer ID centers washer against bolt head bearing surface during tightening. System prevents separating heads, thread stripping, fatigue fractures, stripped nuts, and dished, cracked, or split washers. Coarse- and fine-threaded components range in size from 1/4-11/2 in. dia.