The Pop Up Towing Companion Post Adapter for Flip-Over Hitch adapts to older Companion 5th wheel hitches. It converts from a round hole to a square post for mounting accessories. Does not fit the new model 3500 Companion 5th Wheel hitch rated at 20K. For 3500 Companion use item 144752.ONLY fits Flip-Over Hitches made by Pop Up. This product will not work with the 317 or 318 models. Only fits Flip-Over Hitches made by Pop Up Does NOT fit new model 3500 Companion hitches rated at 20K Will not work with 317 or 318 models | Popup Towing Products LLC Pop Up Towing FLC Adapter Fits PopUp Flip Over System Only