Capture Plates are a required component of the SuperGlide hitch system. When the trailer is hooked up to the hitch, the Capture Plate's wedge isolates the king pin from turning in the fifth wheel plate, causing the Cam Assembly to activate and allowing the SuperGlide to move as turns are being made. Part #3365 fits Fabex and Lippert model numbers 500's, 765, 770, 1621, 1621 HD, 1116, & 1716.Most applications slip over the king pin and are held in place by a set screw. Follow the instructions below to determine your correct Capture Plate.1) Determine if manufacturer name and model number located on your pin box are one of the options shown above.2) To ensure correct fit, make the necessary A, B and C measurements:A: Measure the king pin plate from side-to-side. This is the mostimportant measurement. Be sure that this measurement is no morethan 1/16" less than the measurement listed which is 12 3/4" through 13 1/2" and 14" for part #3365.B: Measure from the leading edge of the king pin to the leading edge ofthe king pin plate. Part #3365 accommodates 2 9/16" through 4".C: Measure from the rear edge to the leading edge of the king pin plate. Part #3365 accommodates all sizes.