Plates that mount to the front axle that corrects for caster after lifting the truck.
The 2.5 version corrects caster for a lift range from 2" - 3" and works with the stock front drive shaft.
The 4.0 version corrects caster for a lift range from 3.5" - 4.5" and works with a Double Cardon front shaft.
To calculate your ride height, measure the distance from the hubs center to the underside of the fender/flare and subtract 20.5".
For ride heights from 3.0"-3.5", the 2.5" plates will be slightly under 2* of caster and the 4.0" plates will be sightly over 4* of caster.
Installing the 4.0" plates alight the pinion for using a DC drive shaft if needed to cancel vibrations on deceleration.
Plates pictured are the 4" version, 2.5" are similar