B9E base
The 9-pin B9E (Novar) tube base is a larger variant of the B9A (Noval) miniature 9-pin base developed for higher-powered American tubes such as the 7868, 6JE6A, etc.
It has nine pins with 1.02 mm (0.038") diameter in a 17.45 mm (0.687") pin circle diameter arc.
The similar B9D (Magnoval) based used by comparable European tubes has the same pin circle geometry but the tube have a diameter of 1.27 mm (0.046"). Inserting Magnoval tubes into Novar sockets by force will widen the latter's contacts, thereby damaging the socket, whereas a Novar tube will not make reliable contact in a Magnoval socket.
Moreover, many Novar tubes have a glass nipple at bottom of tube which requires a center hole in the socket.