Middle Atlantic PROWRK-RR44 The Middle Atlantic WRK Cage-Nut Style Rackrail Kit PROWRK-RR44 is designed as an alternative to the standard 11 gauge, 10-32 threaded rackrails included in the WRK Series of racks. Simply remove the standard rackrails and replace them with this kit to fit your needs. Cage nuts and rack screws must be purchased separately. This model is made specifically for WRK 44U racks.