About half the strength of medium-strength bolts, these Grade 2 bolts are for light duty fastening. A square neck keeps them from turning when tightening a nut. A smooth, rounded head provides a finished look. Material meets ASTM A307 or SAE J429 specifications for quality. Dimensions meet ASME B18.5 specifications. Length is measured from under the head.Zinc-plated steel bolts resist corrosion in wet environments.