For those valves such as EL504 FU519 EF37 6F8G 6J7 that utilise a top fitted cap for it`s anode connection, you will needs ones of these guys. A 6mm, 8mm and 14mm anode caps. 6mm Ceramic, nickel plated Anode Cap6mm Ceramic, nickel plated Anode Cap 6mm Ceramic, gold plated Anode Cap6mm Ceramic, gold plated Anode Cap 8mm Ceramic, nickel plated Anode Cap8mm Ceramic, nickel plated Anode Cap 8mm Ceramic, gold plated Anode Cap8mm Ceramic, gold plated Anode Cap 14mm Ceramic, nickel plated Anode cap14mm Ceramic, nickel plated Anode cap 14mm Ceramic, gold plated Anode cap14mm Ceramic, gold plated Anode cap