Tenons are traditionally cut by hand, and their two surfaces are imperfect. To smooth tenon faces, and ensure a perfect fit into the mortise, a shoulder plane was used. Because the blade of a shoulder plane extended to the outer faces of the shoulder plane’s sides, they cut the full width of the plane. This allows woodworkers to get into the corner of a joint like a tenon. A shoulder plane can also help fine-tune rabbets, grooves, dados and the shoulders of some of these joints. There are typically three sizes of shoulder planes; small, medium and large. The main difference is in the overall width of the plane. A narrow shoulder plane can fit into more joints than a large shoulder plane, but it’s more unstable, and more passes are required to trim the entire cheek of a tenon. Some companies even produce miniature shoulder planes. The low bed angle of a shoulder plane allows it to slice more cleanly into end grain.