I don't think you can get the silicon stoppers to fit under a threaded charm. They fit into some of the spacers and open work charms.
I wear mine with 2 clips and 1 charm in between. I use the silicone stoppers underneath the clips as I like my charms to stay in place.
I find on the bangle the charms whizz around far more than the bracelet.
Don't the clips or charms scratch up the bangle as they move around?
I would think that since the bangle is smooth, a loose charm would quickly show wear and tear.