Our UL-NW-3 is sloted for our No. 58 key. Milled steel, the flat base is .465" wide, by .750" long, with a large surface for a good solder joint, if desired. The base is .050" thick, ideal for thin wall barrels. The blade is 0.075" thick and stands 0.19" above the base. The slot is 0.93" tall by 0.42" long (square the slot to use the full width). Most rifles will use three underlugs, while barrels longer than 42" use four. Made in the U.S.A.