Our UL-36 lug is milled steel, for standard sized keys. Popularly used on Hawken and similar Plains rifles, the slot measures .5" x .12". It fits our favorite KEY-36-B or I as cast. Some gentle peening can compress it, to hold thinner keys snugly. The dovetail is about .75" long by .5" wide. Mount it to the bottom of the barrel in a 0.050" deep dovetail.