Finish doorways, wall ends, kneewalls, and closets by eliminating the need for the drywall face and 2 corner beads. 4 5/8" Fast Cap is designed for 2 x 4 wood studs only. 4 7/8" Fast Cap can be used with wood studs or 3 5/8" metal studs. Archway minimum 15" inside radius or 28" outside radius.