Rotary valve bumper stop, neoprene or natural cork. 1 foot of Conn & King, French Horn, Trombone, Tuba rotary valve rubber stop, bumper stock. 11/64" pair, 3/16" (4.7mm common, YBB Tuba), 1/4" (6.4mm older, Jupiter Tuba), Round 9/32" (7.14mm). Or choose a stick of 1 1/2" x 3/16" natural cork (round).
Cut your own, round neoprene.
Part numbers, Conn SP08130, A200; A201, A203, A470 (cork)
