Silicone gripper for DTR(left) or CATII(right)
the grippers are about 35mm  in diameter on the inside
 
replacement/upgrade parts for the catii or dtr 
dtr: https://foreskinrestore.com/dtr/
catii: https://catstretcher.com/
 
All my silicone items are made with dragon skin silicone from smooth-on and it is certified skinsafe.