HO-Scale Package Includes: (2) Pair #178 Scale Whisker® Metal Couplers - Medium Centerset Shank (2) Pair #178 Scale Snap-Together Gearboxes and lids (2) #625 Knuckle Springs #178 Scale Whisker® Metal Coupler Features: Material - Metal Shank Length - Medium (9/32") (center hole to back of coupler head) Coupler Offset - Centerset Knuckle Spring - #625 Centering System - Whisker® Head - Scale Head #178 Snap-Together Gearbox Features: Material - Insulated Plastic Lid Type - Snap-Together Dimensions - 19/32"L x 17/64"W x 5/32"H Mounting Specifications: Mounting Height - 29/64" Centerline - 25/64" Trip Pin Height - 1/32" Center Hole - 2-56 Insulated Screws are the most commonly used. (Screw length will vary) Rear Hole - 0-48 or 0-80 are the most commonly used. (Screw length will vary)