edge of the ring has worn application_number US 93117786 A description now referring to the figures and more particularly to fig1 3 false twisting unit 1 of fig1 includes three vertical shafts 4 5 6 each mounting three composite friction disks or rotors that is rotors 1 39 2 39 3 39 are keyed to shaft 4 rotors 1 34 2 34 3 34 are keyed to shaft 5 and rotors 1 34 39 2 34 39 3 34 39 are keyed to shaft 6 keyed to the respective shafts 4 5 6 below their respective bottom rotors 3 39 3 34 and 3 34 39 are the respective pinions 4a 5a 6a whose teeth are engaged by the teeth of closed loop timing belt 7 driving power for false twisting unit 10 is introduced through drive whorl 8 that is keyed to shaft 5 below pinion 5a so that whorl 8 drives shaft 5 directly and acting through timing belt 7 and pinions 4a 5a 6a drives shafts 4 and 6 in synchronization with shaft 5 all of the friction rotors 1 39 2 39 3 39 etc of fig1 and 2 are of the same construction which is explained in detail with reference to fig3 which illustrates rotor 1 39 the latter includes base disk 9 and replaceable composite ring 10 that is removably mounted on base 9 ring 10 includes annular support part 11 having peripheral formation 11a that is embedded in friction covering 12 the inner edge of support part 11 is provided with annular shoulder 10 39 that is force locked and form locked to annular shoulder 9 39 of base 9 the connection between shoulders 9 39 10 39 remains secure for extended periods.