Typically these are used on the rear axle to better align the axle and t-case angles, but I needed them on the front to correct a very positive caster angle. Too much caster angle can cause an impact shimmy when hitting a bump. It's very annoying and can pull the wheel out of your hands for a split second before it self corrects. If you're truck is doing this, you likely have too much positive caster on the front axle. I went with 4deg shims and this nearly eliminated the impact shimmy. 5deg probably would have been just a little closer, but this also really helped the front driveshaft angle as well. On my truck, all of this was caused by longer than stock shackles (trailing shackles, not leading ones).

They worked perfectly! Brought the caster to right where it needs to be. Thank you

Using the calculator, it was decided that I needed 10 degree shims on the rear of my 1979 CJ5. The only 2 mods that I made were that, because I didn't like the fact that the pin through hole was not counter-bored to allow the head of the bolt to sit flat, I milled a flat spot on the shims.
The second mod...I painted them!
After installation, the pinion is about 2 degrees below driveshaft centerline, and the vibration is gone.

Shims worked good. The supplied pin head was to big for dana 35 axle. Had to grind it down some to fit

91YJ, in-line 6, 3.5 inch lift, SYE, 32 inch tires. The 5 degree shims on the rear leafs seem to line up everything as needed. Pinion about 3 degrees below the drive shaft angle. I have 6 degree shims as well but if I used those I think it would have put the pinion in direct line with the driveshaft which would be a problem with the possible axle wrap. Agree with other comments, I had the reuse my old pins as the new ones were too thick for my leafs and I would have needed to drill out the leafs and grind down the top of the pin because it was too tall. Overall good to go. Good purchase.