disc 25 can be adjusted by displacement of the adjusting rod set 30 the clamping roller 27 is rotatable and is arranged at the main support 21 for pressing against yarns around the yarn disc 22 refer to fig1 and fig1 this embodiment is disposed on a knitting machine in a similar way as the embodiment mentioned above the difference between this embodiment and the above one is in that friction damping is from the belt in this embodiment in both embodiments the main support 21 is arranged with a bearing 3 therein the main shaft 211 is disposed with the yarn disc 22 and the rotary disc 25 respectively after being passed through the main support 21 to form a linked rotating mechanism then another bearing 3 is mounted in the clamping roller 27 so that the clamping roller 27 is rotatable and able to press against the yarns on the yarn disc 22 the yarns can be metal yarns 4 or textile yarns 5 next the support fixing member 28 of the rubber set is fastened and fixed on the main support 21 the adjusting rod set 30 is passed through the guide slot 281 of the support fixing member 28 the adjusting rod set 30 consists of an adjusting bolt 301 and a locking nut.