... ,6.8,8.8,9.8..... Hollow Bolt,Stainless Steel Hollow Bolt,Bolt with Internal Thread.1.What’s the specification of our Products ... accordingto customer's demand .Threads/ScrowsType "M","UNC","UNF","BSW"thread are available. Head typesHexagon head,Mushroom head,Pan head,Countersunk ... professional manufacturer with more than 20 years experiences in screw,bolt,nut,washer,rivet, stud, pin,wrench and so on . ...