Square Head Bolt, 18-8 Stainless Steel, 1/4"-20 Thread Size, 1" Lg, 50 PK, Midwest Fastener, Mfr#: 53703

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.