This is a fuel filter wrench for 2001 to current GM Dodge Duramax. When replacing the fuel filter the water-in-fuel sensor located in the bottom of the filter must be removed and reused in the new filter. This wrench has two sides, one designed to fit the odd shaped 40mm 12 sided sensor found on 2001 to 2010 trucks, the other end fits the 42mm 6 sided sensor on the 2011 to current trucks.