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Assembly guide can be found here: https://www.youtube.com/watch?v=n5AyakrCIl0
The Key Carry comes with 2 sizes of washers. If using 5 keys then there's no need for the washers, for 4 keys use the thinner washers and for 3 keys use the thicker ones. For 2 keys, use the 3 thicker washers.
The screw that holds the keys in place needs to be correctly tightened. See 1:24 in the assembly video at the top of the page.
The screw shouldn't be flush to the bottom or protruding through. It should be slightly recessed with the silver threads not visible (if one thread is visible this is ok). If multiple threads are visible then a thinner washer(s) need to be used to allow the screw to thread further in.
How tight your key carry holds your keys is up to you. I find having it so the keys can't flick out under their own weight works best for me.