Used to block light from escaping around shifter stem seal. Fits 1969-73 Mercury Cougar and Ford Mustang as well as 1971+ Pinto, Bobcat, Maverick, and Comet with floor shift automatic transmissions. The 90 degree notched portion straddles the set screw on the cast light housing. Most shifters (almost all) we see do not have this part in place any longer. Ford part number C9ZZ-7E130-A.
Check out our video on rebuilding your shifter below: