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 in, 3-1/2 in or 4 in octagon box or any plaster cover with mounting holes on 2-3/4 in centers. 6 in and 10 in bells also mount on 4 in square boxes. Specified for timing, scheduling, paging and general alarm applications. 4 in sizes recommended for quiet office areas. 6 in sizes for moderate noise level areas such as general factory areas. 10 in sizes for loud areas such as heavy machine shops. Universal adaptaplate mounts directly on surface or electrical box Weather-proof by adding appropriate back box Completely assembled, all hardware supplied Self-compensating solenoid plunger Rated 400 hr at 50% duty cycle