8-18X2 1/2 Square Recess Round Washer Head Self Drilling Screw Full Thread Zinc (Pack Qty 2,500) BC-0840KQRW

Common usage is to attach plywood, soft wood or metal to tmetal. The wider head design offers greater protection to the mating surface while supplying excellent torque transmission that resists cam-out AISI 1016 - 1022 or equivalent steel