Keeps octal based 5U4GB, GZ34, 6L6GC, 6V6GC, EL34 and other octal based tubes from falling out of their sockets. Nickel plated spring steel; four small teeth grip the tube base securely. Mounts to the chassis by the same screws holding down your tube sockets. I measured 1.530" mounting centers. Slotted mounting holes allow some latitude of installation. The same type of tube clip has been used on many old and new Fender guitar amps. Set of four.