This are the Fox 2.5 CO's 2-3" lift for the 4th gen 1500, single collar adjuster,
Fox 2.5 coilovers
Quick shifter is showing us the 4-6" ones here, also single collar adjuster
BDS/Fox 2.5 coilovers
If you want to compress the spring you may need to remove the CO, compress the spring, adjust the collar and put everything back. Again i won't judge your methods. I'm not a a certified machanic and i haven't screwed it up in years since i've been adjusting my coilovers in multiple applications. sure compressing the spring is safer.
Fox uses a similar collar to Icon, most important thing is to remove the wheel from the vehicle, loosen up the pinch bolt 1 full turn, the turn the collar. Contact Fox to know exactly how many turns you'll need for 1", with King is 0.2" per every full turn. It might be different with Fox.
Fox threads seem a little smaller compared to King
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2020-12-04_09-35-57 by
RAM RSM, on Flickr
so you may need more turns to achive 1" lift. Per the video below from Icon, they say 4 turns for 1/2" and that partiucalr Icon CO feature similar threads to the Fox shocks for the RAM 1500, at least the 4th gen one. We haven't seen the new 6" for the DT truck., Fox can confirm for you.