5/16-18 x 1-3/8 Zinc Plated Steel Coarse Thread Battery Bolt (50 pcs.)

Diameter: 5/16"
Length: 1-3/8"
Material: Steel
Finish: Zinc
Head Style: Square (1/2" Wrench)
Thread Size: 18 (Coarse)
Hardness: Grade 2 / A307
Type: Square Head Bolt

Box of 50.

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.