These HD wheels work inboard or outboard with BOP plastic delete 4th wheel spacer kit for the 19+ Viper & Sidewinder with 25mm axle. These HD wheels will not work in the inboard loaction with the factory axle spacers as they are wider. 129 and 146 skids requird 7.125". All others are 8" After some test fit ups these wheels can now be used on the outside of 19+ models with the 25mm axle. If using these in the outside location on axle, (2) shim washers are to be installed between axle and oem washer on each side.