I don't use anything to fix it to the button to the top and I've never had any problems with it coming lose or taking it off to clean. Very high quality, like all things Reo.
Here's a tip:
If you want to tweak the height of the button to taste, clip off a corner of a business card or two and then start clipping off small bits of the corner until it fits into the button top snugly. I use 3x stacked card corners to get the feel I like just right.
also I recommend to only use 100% genuine REOSMODS.COM business cards for absolute maximum quality
-sent form my mobile phonnr