This K Series thermostat is designed to bolt directly to the water pump housing. It offers the same -16AN port to easily switch coolant fittings (1.25" Hose, 12AN, or 16AN). It also rotates 360 degrees allowing you to position the outlet to fit your setup perfectly. What is different with this housing is the two 3/8NPT ports located behind the thermostat. These allow you to properly run the recirculation hose and heat. This is important because when the thermostat is closed coolant will still be able to flow through the ports behind the thermostat. This will offer proper warm-up with coolant flowing from block to head while the thermostat is closed (same as OEM design). There is also a 1/8 NPT port for optional sensor (plug included) and a blind port for Fan Switch. This is not fully drilled so no plug is needed. However, if you want to run fan switch simply drill a hole in the center. The port is already tapped.