The System Sensor Flow Switch WFDT Retard T-Tap is a vane type waterflow alarm switch for use on wet sprinkler systems that use 1" (25mm), 1 1/4" (32mm), 1 1/2" (40mm) and 2" (50mm) pipe size. This unit is UL Listed and has a 25mm threaded connection and can be mounted in the vertical or horizontal position. See Technical Data Sheet for more information regarding this product.