The seat ring provides a stable, uniform and replaceable shut off surface. Seat rings are usually held in place by pressure from the fastening of the bonnet to the top of the body. This pushes the cage down on the lip of the seat ring and holds it firmly to the body of the valve. Seat rings may also be threaded and screwed into a thread cut in the same area of the body. Seat rings are also typically beveled at the seating surface to allow for some guiding during the final stages of closing the valve.