This self-centering doweling jig comes with six removable screw-in bushings. Sizes are 1/4, 5/16 and 3/8 (2 of each size.) This permits the user to drill two holes parallel to one another on 3/4 in center for double dowel applications. The 7/16 and 1/2 holes are permanently drilled in the center guide that has a 6 in wide capacity. Made from aircraft grade aluminum and steel then plated for corrosion prevention. Made in the USA.