This vacuum advance lockout mounts to the distributor and is used when switching from a vacuum advance to a mechanical advance.{specs}.
PROFORM #67022C DISTRIBUTOR VACUUM ADVANCE LOCKOUT REPLACES VACUUM ADVANCE
Distributor Vacuum Advance Lockout; Counter Clockwise
NEW 53 54 55 CORVETTE DISTRIBUTOR VACUUM ADVANCE 235 BLUE FLAME 1953 1954 1955
6000 Series HEI Distributor Vacuum Advance Canister
7000 Series Distributor Vacuum Advance Canister - Counter-Clockwise Rotation