Fits models: 4516 4513 4013 4556 4553 4053 457 Shorty .45 - Will NOT fit: - Shorty .40 - CS45 - These are compact single stack magazine (short grip) .45 and .40 caliber semi auto pistols - Our grips are a two piece that replaces the one piece stock grip. These grips are a curved backstrap design that installs using a mainspring retainer and screws which come with the grip. The mainspring retainer is pinned into position with the pin that holds the stock grip on. The mainspring retainer provides the threaded bosses that the grip panels screw into.