Standard Medium Centreset ShankThis industry leading coupler features Original Style Head Medium Centerset Plastic Couplers, and 850 O Scale centering spring and comes complete with Plastic Gearboxes and lids. The 804 Plastic Coupler may be mounted with the included 817 Plastic Gearbox or 818 Metal Gearbox (sold seperatly), 819 Extended Metal Gearbox (sold seperatly).It is not recommended to use a metal coupler directly on a metal surface or in a metal draft gearbox to avoid possible electrical crossover and shorting that may cause damage.One pair per packageSimple Drop in DesignTrouble Free OperationCompatible with All Kadee® O-Scale CouplersWorld-Renowned Quality & PerformanceThey just Last & Last & Last...Package Includes:(2) Each 804 Original Style Plastic Couplers - Medium Centerset Shank(2) Each 817 Plastic Gearboxes & lids(3) Each 850 O Scale Centering Springs