These are made for the '89 11.75" Bronco 5 on 5.5" rotors and an 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 and wrap completely around the axle. If the were only partially around the axle they would be strong enough but welding the entire diameter helps control warp of the tube itself. These are made for Full Floating Spindle end axles but will work with the factory flanged axle ends, just turn the flange down and cut off the bottom half of the circle.
Sold in pairs.
NAPA Part numbers for '73-'87 3/4 Ton Front, 4x4, Chevy Calipers and Rotors:
Caliper ONLY: LH - N4674, RH - N4673 - Both of these are LATER year part numbers
LH - N4597, RH - N4596 - Both of these are EARLIER year part numbers
Ford 9" Rotor - NB 4885611 Premium Rotor
UP 85611 Ultra Premium