Image Item No. Description  2685b  Monorail Coupling Long (Sets 6399 / 6991) Catalog: Parts: Monorail  2685a  Monorail Coupling Short (Sets 6990 / 5040) Catalog: Parts: Monorail  2684c01b (Inv)  Monorail Motor 9V with Long Couplings Catalog: Parts: Monorail  2684c01a (Inv)  Monorail Motor 9V with Short Couplings Catalog: Parts: Monorail  2684  Monorail Motor Base Catalog: Parts: Monorail