This is one of those things you realize you need once you start carving skulls for the first time. You can only hold onto a Dremel for so long before the thing starts getting in your way and your fingers get tired. An rotary extension feels more like you are holding a pen and gives you more flexibility. There are only 6 items in this list, but I think this is a must for carving animal skulls. So i ordered a pair of it.