... , round type and hexagonal type,This hollow hole are usually named flushing hole, used for transmitting water ... sleeves, shanks or bitsUsually for extension rods, there are R22,R25,R28,R32,R38,T38,T45,T51, ... ST58,GT60 threads, and different length of rods are available from 600mm to 6400mm usually. Product NameDia ... T511830T51-T512435T51-T513050T51-T513660 T51 Drill Rod in high quality and factory prices