A window on the side of the jig makes it easy to make perfectly matched butt or miter joints, rail joints, even mortises. With 4 tapered holes and 6 hardened steel bushings (2 each 1/4", 5/16" and 3/8".) Holes 1/8" to 3/8" can be drilled side by side on 3/4" centers without moving the jig.