The “bolt” head is 3/4″ diameter with no spanner flats, relying on flats engaging with the brake anchor slot to prevent it rotating. The threaded portion of the bolt is 11/16″ long and is 1/2″ diameter with a 1/2″ cycle thread. The long shanked domed nut is 1 1/4″ long and 3/4″ diameter on its shank. It also has an undersized head that takes a 7/16″ BSF spanner. The hole in the frame lug is 1/2″ dia. and there shouldn’t be a gap between it and the brake anchor plate. Check your rear wheel alignment.