The caster wheels sit in the felt pads but not snug so when you move/roll the chairs they come right off. The caster wheel comes off when the chair is rolled.
Neat invention. Highly recommended. Thankfully, where there's a need there's usually a product. I am sure it's only a matter of time before the extras come in handy!
They have nice deep grooves to hold them in place, and i feel like the grooves and the semi-soft plastic will keep them from slipping. I like that the ridges were on each side. They grip too, so that was awesome, plus you can't tell they are there.
They are transparent, so they're not jarringly obvious when in use. They are translucent and kind of a thick almost gummy bear like consistency.
They are wedge shaped, but you cannot hammer them under anything!