The 2013 Ford F350 4X4 Regular Cab Dually bolt pattern is 8-200 mm. This means there are 8 lugs and the diameter of the circle that the lugs make up measures 200 mm or 7.87 inches across. To get a close measurement of your 8 lug bolt pattern without a bolt pattern tool you should measure from the center of one lug to the center of the lug across from it.
