I somehow split one of the original green vinyl end caps that had been added by Riffclown. So I switched to a black one I had in stock. The end caps I used are .313" I.D. x .75" long. After trimming off the end I stretched them a bit by placing them on needle nose pliers & pulling the handles outward. Rotated them & did that four times. Then I lubed the end of the vertical with saliva & slid the vinyl down into position. After the vinyl regained it's memory the end cap is tight on the tube.