That's unfortunate. I would have assumed that they would work in most Halo 5" and 6" recessed cans since they are a major and common manufacturer.

I had the same issue it says works for 5 and 6 inch cans but for the life of me I could not figure how to make this work in 5". I guess i will return these to the store.

No, you should not return them. I too thought it would not fit a modern can of 5", even though the package says it would fit. The trick is look for a secondary hole above and inboard of the hole the spring clip is now in while the light is facing down while resting on a table. Remove the screw that holds the spring clip in its current location and remove it and install in the location I identified above. That is the 5" hole and it will fit perfectly, as it does for the 6" can. It really will work for a 5 or 6" can like the package says. Hope that helps. BTW, these are much cheaper at Costco than they are at Home Depot or Lowes.