I bought these sponges to maintain the parts of my rifle so as not to damage the metal parts. It comes with 2 magnetic covers with very good magnets. When they're in a vise, they don't move until I move them. These jaw covers are specially designed for 4 inch jaws and the coverage is accurate. The flat jaw cover is ideal for holding an upper or lower vise block without damaging the teeth of your expensive tools. The ribbed lid holds kegs or pipes in place really well and with a good grip. The density of the lids is just right to provide both traction and cushioning. They can be swapped out or removed in seconds. I find it practical that they stick together when not in use and do not get lost when stored. I looked at various cheek cases before settling on this one and I think they fit my needs as a gunsmith perfectly.