For the KingPin 4, this part isn't necessary. The KingPin 4 male portion has a removable sleeve to allow it to fit a 2-inch female receiver. Just remove this sleeve and it should fit the 1.25-inch female receiver. Please note that the Draw-Tite 1.25-inch for a 2012 Prius V will not work with this adapter without some "manual" changes. There is a notch that prevents full insertion of this part.