These short bed extended couplers add nine inches more clearance between the truck cab and the trailer nose, and between the truck tailgate and the trailer bulkhead. They fit standard gooseneck receiver tubes. The GN8 2-5/16" V-19 28,000 pound rated coupler latches when lowered onto the ball, and releases remotely. You really need this extra clearance for towing a full-nose gooseneck with a short bed pickup. The extra trailer swing is a cab and rear window saver. SB1 - 4" Round Coupler 9" Offset SB2 - 4-1/2" Square Coupler 9" Offset SB116 - 4-1/2" Round Coupler 16" Offset SB21 - 4-1/2" Square Coupler 16" Offset SB3 - 4" Square Coupler 9" Offset SB316 - 4" Square Coupler 16" Offset