Square Head Bolt, Steel, Grade 2, Zinc Plated, 3/8"-16 Thread Size, 4" Lg, 10 PK, Midwest Fastener, Mfr#: 71728

A square head bolt has a four-sided head. Compared to standard hex bolts, square bolts have a greater surface in contact with the part being fastened, and therefore provide greater resistance to loosening (though also greater resistance to tightening). Square bolts are typically mated with square-headed nuts.