... are made by hollow drill steels, there are two shapes of extension rods, round type and hexagonal type,This hollow hole are ... be used for connecting coupling 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 ...