The Standard Mount attaches easily to any tubular standard or powered wheelchair back post from ¾" to 1" diameter, even over fabric. The Backrest Mount attaches directly to the back of plastic or metal molded backrests. The Keyed Back Post Mount is for wheelchairs with keyed back posts. All three adjust vertically 8", and the articulated arm adds up to 6" of A/P adjustment. The extra space allows for clearance around other equipment attached to the back posts or to accommodate special seating systems. Mount base allows the relocator with mobile arm support still attached, to be removed and replaced without tools to its original pre-set position