This industry leading coupler features New Generation AAR Type "E" "Prototype" Head Medium Overset Metal Couplers, and #850 O Scale centering spring and comes complete with Plastic Gearboxes and lids The #742 Metal 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.