Easily clips onto the rim. Better I think for small toms. There's a standard size that's better for snares. Can clip them onto the resonant head too, to cut any buzz.

This little gadget is small but has a huge change to your kit. My floor Tom had a ring that was just too much. I tried moon gels that I use often but they didn't give me the tone I was looking for on my floor Tom. A friend had a few of these and showed me how they made the tone just right. I still wanted some ring but not too much and gels just took out too much ring for my taste. This was a definite smart invention that should be at the top of the modern drummers list.