Universal brass instrument valve stem or finger button, cork washers, each purchase gets a set of 3, you choose your size.  see my item ID# 275667836939 for thicker stem corks typically used on Conn Tubas & Sousaphones, licke the 20K.

Cork 1/2" OD x 1/16" thick x 7/32" ID.  Most common cornet & trumpet.

Cork 9/16" OD x 3/32" thick 7/32" ID.  Most common low brass.

Cork 9/16" OD x 1/8" x 7/32" ID.  Many horns needing thicker cork.