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
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
7000 Series Distributor Vacuum Advance Canister - Clockwise Rotation