Tube Socket Noval, top mount w/shield

The metal shield base fits over the porcelain socket in only one way, by lining up the opposing grooves in the socket with the indents the base. Then the tube shield slides in over that and locks into the
Note the socket is designed for top-mounting, where the chassis is sandwiched between the socket and the shield base. The latter is screwed into the chassis, and the tube holds up the shield.