Thicker domed head provides greater wear resistance.
Specialized head diameter provide for a tighter fit in countersunk holes
Head design will fit into all applications designed for # 3 Heads.
Deeper depth of square provides fuller engagement.
Smaller transition angle on the corners of the square provides for a greater resistance against spinning in the hole during installation.
Tighter tolerance on the body diameter for sizes 5/8 and larger, minimizes the potential of the bolt moving in the hole, which can result in the assembly coming loose and causing rounding out of the installation holes.
Grade 8 (per SAE J429) - 150,000 psi minimum Tensile Strength Heavy Duty, Best Strength to Toughness Ratio