The #158 "Scale" All Metal Self-Centering "WHISKER" Coupler features a "Scale" Metal Coupler (a smaller head coupler which is more to scale and is patterned after the type 'E" couplers) and Metal "WHISKER" Centering Spring, insulated Draft Gear Box and Lid. The #158 Coupler may be mounted with the supplied #242 draft gear box (Not included with the Bulk Packs) or with the manufactures cast-on coupler pockets. The coupler will couple and uncouple with Kadee's other HO and HOn3 couplers. The coupler has the same shank length as the #5, #28, #38 or #58 coupler which will allow the modeler to remove the existing #5, #28, #38 or #58 coupler and replace with the new smaller coupler. The #158 coupler is made of the same metal as the #5 & #58 for strength and rigidity. The #158 package contains two pairs of the new coupler, two pairs of the #242 gearboxes, and instructions.It is not recommended to use a metal coupler directly on a metal surface or in a metal draft gear box to avoid the possible electrical crossover or shorting that may cause damage. Use the provided insulated draft gear box.