... .8,9.8........ WAVE PLATE HEAD SCREW,DOUBLE HEAD SCREW,KNURLED HEAD SCREW A good non-standard fastenerS ... Machine threads.Head typesHexagon head,Mushroom head,Pan head,Countersunk head,Bugle head,Oval head,Hex flange head,Round head,Ball head,Button head...Socket typesPhillip ... Head is much thicker ,it is strong not break down . meanwhile,socket is much deeper,it is convenient to tighten by screwdriver ...