7018128 (Watts) | 2-1/2 - 4 Inch | 757/757DCDA First Check KitThis 2 1 2 to 4 Inch First Check Kit is Made to Repair a Double Check Detector Assembly Used Primarily on Fire Sprinkler Lines When it is Necessary to Monitor Unauthorized Use of Water And to Help Prevent The Backflow of Pollutants That Are Objectionable But Not Toxic, From Entering Into The Potable Water Supply. It is Designed For Non Health Hazard Applications And May be Installed Under Continuous Pressure Service to Protect Against Both