These units are designed to be mounted to a universal flat-bottomed slider for fore and aft movement. It has a square 6.5x6.5 inch flat top with universal mounting holes at each corner. The Post swivels 360° with auto lock forward facing feature. Proper orientation is required for installation. The round base is a standard 8 1/4” 6 hole bolt pattern with 9 1/4” OD.