Ignition switch with 2 keys.
As used on many late 1960's/early 1970's models, including :-
AJS, Matchless 750cc
BSA B25,C25,B40,B44,A65,A75
Norton Atlas, Commando (-1970)
Triumph T100,TR25,TR5,TR6,T120,T140 etc
Part numbers: 30608, 31403, 31899, S45, 60-989, 99-0558 and S45