Direct replacement for all Genie Chain Drive door openers with steel T-Rail assembly. Older part numbers 21784R, 20438R *IMPORTANT* If replacing older carriage with T-Handle you will need part 25605R inner slide also. Direct replacement for all Genie Chain Drive door openers with steel T-Rail assembly. Older part numbers 21784R, 20438R *IMPORTANT* If replacing older carriage with T-Handle you will need part 25605R inner slide also.