*Must have* for the Duffalo bar (my setup is ML rack). These greatly improve quality of life when using the bar. I used to get extremely frustrated with all of the issues from using the Duffalo bar on normal Jcups or Ghost rollers on my ML rack. These fix everything. These work fine for flat bars, too: the inserts rotate so that they can accommodate both the cambered Duffalo bar and a regular flat bar. I use my ghost j-cups with Duffalo inserts for both squats and press. One less thing to change across exercises. Note however that it is NOT feasible to swap back and forth between these inserts and the stock rollers. You're effectively changing your Ghost jcups permanently. It takes quite a bit of force and time to break loose, remove, and reinstall the bolt. It's not quick and easy to swap them back out. No way I'd consider changing them across exercises or even different training days. To that point, be prepared to buy a second pair of Ghost jcups if you want the stock rollers for other bars. Final note: I sometimes have the "sticking" issue others have noted, but I think it could be due to temperature changes when I leave the bar out overnight on the rack. It happens to me when unracking the bar empty or with two plates for my first warmup sets. But it doesn't get stuck thereafter. I also think it could be due to how one unracks. It's forced me to be more aware to apply equal force with both legs when unracking. If it does get stuck on one side for the first warmup set or two, unracking straight up with both legs seems to do the trick.

The blocks are a must for squatting with the Duffalo bar. I haven't experienced the issue that some other reviewers have had as long as the bar is recentered between sets. Otherwise, if the knurling sits within the block, there could be a problem with sticking. I highly recommend this product to anyone who uses a Duffalo bar.

I bought the Ghost j-cups and blocks to improve my safety while lifting with a cambered bar. I agree; it is very unnerving that one of the blocks would not let go of the bar out of the box. It was to the point that I felt it would not be safe to lift if I were under a working load. I broke out one of my files and loosened the block's parameters. I think I about have it now and am looking forward to my first workout with them. I agree with another commenter on encouraging Ghost to improve the design to allow for the use of blocks and rollers. The rollers look lovely, and I would not want to buy another pair of j-cups to use them and the camber blocks in the same workout. If you're going to tweak the blocks a little out of the box, I say buy them. They provide an excellent shelf for the bar to sit in. Cheers.

Didn’t realize you needed to remove the screws, washers and rollers and to swap in the blocks - makes it a bit of a hassle when you use your j-cups for multiple bars, and defeats the purpose of having the rollers all together if you decide to keep the blocks in. Would be great if they figured out a way for the blocks to sit on top of the rollers, making it much easier to swap. The way they are designed now is sort of a semi-permanent change. Still, they do what they are meant to do.

I’ve used the blocks with my Duffalo bar a few times now and the cups seem to be cut too small. The bar sticks in one or both sides when being lifted out. With weight on the bar this is really unnerving as it throws the bar off balance. I guess I’ll try to sand the cups some to make the opening at the top larger but this seems like a design/production flaw. I never used the Ghost-made blocks so not sure if this was an issue with the originals or just something with the new Rogue versions.