This 5/8-18 x 2 hex washer head bolt with a flat bearing surface is made of high-alloy steel. Primarily used on truck frames, this bolt's flange eliminates the need of washers and helps compensate for a misaligned hole. Typically used with a Grade G locking flange nut, the bolt system resists bolt slippage by distributing the clamp load over a wide area. The bolts shall be heat-treated, oil-quenched and tempered at a minimum temperature of 800 degrees (F). Being Grade 8 strength, the Proof Load is 120,000 PSI with a minimum Yield Strength of 130,000 PSI and Tensile Strength of 150,000 PSI.