... the threads can 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 ... MF1830R32 MF3050Round RodsRd38R38-R38280R38-R381220R38-R381830R38-R382435R38-R383050R38-R383660Round Rods & Round MF rodsRd38T38-T381220T38-T381525T38-T381830T38-T382435T38- ...