The Lyman™ 17ATC Target Front Sight For T.C. Rifles is machined from a solid piece of steel. Height is measured from the bottom of the dovetail to the center of the aperture. Includes 8 target inserts that are locked in place with a threaded cap. Inserts include 2 post inserts (.050" and .100" wide), 1 bead insert (.062") and 5 aperture-type inserts.