AC vibrating bells produce a long continuous ringing sound. The striker continues to strike the gong in rapid-fire action as long as current is applied. Universal Adaptaplate mounts directly on surface or fits any single-gang box, 3 1/4" (83 mm), 3 1/2" (89 mm), or 4 " (102 mm) octagon box, or any plaster cover with mounting holes on 2 3/4" (70 mm) centers. 6" and 10" bells also mount on 4" (102 mm) square boxes.