... 8.8,9.8........ WAVE PLATE HEAD SCREW,DOUBLE HEAD SCREW,KNURLED HEAD SCREW A good non-standard fastenerS ... threads for 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 type, ... 23% ,is higher hardness than other.2.Fasteners' Head is much thicker ,it is strong not break down ...