Pair of black neoprene rotor stop bumpers for use on Bach Stradivarius and Artisan series tenor & bass trombones using standard rotary valves. These pieces have an "omega" shape with a circular portion that's approximately 19/128 (just under 5/32) in diameter (3.69mm). See image for more. If out of stock, substitution option is our item 113554 Universal Rotor Stop Bumpers, Round w/Flat Side - pair