... . 2)This design provides a fast drilling rate and added cutting structure durability in medium-to-medium hard formations.3)The HSN rubber ... to minimum.Main Type AvailableSize: 2 3/8",3",3 5/8:",3 7/8",4",4 1/2",4 5/8",4 3/4",6",6 1/2",7 1/2",8 1/2 ... ",9 1/2",9 5/8",9 7/8",12 1/4",15",15 1/2",17 1/2", etc ...