Apparatus for use with a bolt and nut to hold down a water closet to a flanged member with a slot therein, which is economical to produce and install. The fastener assembly includes a sheet metal member with a center portion bent into a U-shape for reception in said slot to resist turning, a hole in the center for receiving the shank of the bolt so it can project through the slot and through the water closet, and turned-over ends for engaging the bolt head to prevent it from turning. The assembly also includes a cap with an upper washer-like portion through which the bolt shank can project and flared side walls whose lower end can rest on the water closet, and a cover with tapered inner walls for snugly engaging the side walls of the cap.