OPW FC MFPD DEF Mis-Filling Prevention Device, Adapter Only

A fixed magnetic field within the Mis-Filling Prevention Device actuates a magnetic interface in the spout of the 21Gu nozzle to allow the flow of DEF. Without the Mis-Filling Prevention Device, the DEF nozzle will not flow. Putting the nozzle in the wrong tank, say your diesel tank, the nozzle will not flow. No other DEF-filling nozzle has this DEF mis-filling protection capability. 
The MFPD is located inside the vehicle DEF fill pipe