These are possibly the most popular rotary bit used by carvers. They consist of a metal core with small particles of ruby bonded to the surface. Originally designed for carving certain plastics, they work well on many types of wood including basswood, butternut, cedar, jelutong, pine, cedar and tupelo. They are durable, controllable and reasonably priced. Available in 3 grades: Standard, Rubynit (coarse), and Super-coarse. 3/32" shanks.