Bach Trombone, Rubber Valve Stop Bumper, 1 Foot, or set of 2 pieces. Bulb is 4.0mm.
Fits many Bach tenor trombones, including an older Holton H179 French Horn (1960s) and a TR-650 Holton Collegiate G-trigger trombone. Contact me if you wish to verify your model's fit or you need other parts.