These can be used on 3.25" diameter axle tubes and are made for the 11.75" diameter Bronco 5 on 5.5" rotors and the inexpensive '73-87 Chevy 3/4 ton 4x4 front caliper. You can use any of the 20 or so high performance calipers that share the 7.05" caliper pin spacing also but the Chevy seems more than good enough for nearly everyone.
These are 3/8" thick
Sold in pairs
Requires steel wheel 15" with a maximum 4" back spacing
NAPA Part numbers for Front 4x4 Chevy Calipers and Bronco Rotors:
Caliper ONLY: LH - N4674, RH - N4673 - Both of these are LATER year part numbers
OR
LH - N4597, RH - N4596 - Both of these are EARLIER year part numbers
Ford 9" Rotor - NB 4885611 Premium Rotor. To use as a slip over rotor you may need to turn down your axle shaft flange
UP 85611 Ultra Premium
WARNING: This product can expose you to chemicals including lead, which is known to the State of California to cause cancer. For more information, go to www.P65Warnings.ca.gov.