This Adjustable Bag Rider made by Long Shot Precision is designed to clamp to an MPR Monopod Rail (sold separately). This bag rider provides the same superior functionality as other A.B.R.s. The custom dowels ride in linear bearings for consistent smooth operation. A custom-designed SS thumb wheel rides in two Delrin thrust washers that are known for their strength and creep resistance. The ABR replaces the need for expensive, heavy, and bulky adjustable front rests and wobbly monopods. Installation is simple, quick, and you never need to remove it.