Genuine AC Delco Water in Fuel (WIF) Sensor. Great to keep as a spare because if you destroy the one you have removing it from the bottom of the fuel filter the truck is inoperable until the sensor is replaced! In the picture the PPE WIF Sensor Wrench is shown removing the WIF sensor from the fuel filter.
If your WIF sensor is all chewed up from trying to use channel locks, click the WIF Sensor Wrench link and add one to your order. You'll be happy you did!