The MSN 120 is a super bright, daylight visible strobe light that can not be ignored. It is designed for use as an alarm light. It requires only a 3/4" knockout (1-1/16" diameter hole). It can be installed on panels up to 1/4" thick. We've modified the connection barrier to simplify wiring. Large mounting nut for easy installation. UL Recognized. For use in Type 3, 3R, 4, 4X, 12, and 13 environments.