Now when it comes to the actual engraving bits, there are an incredible amount of different types. However, in this article, we'll simplify things and go down to two basic ones - metal and Plexi. For steel/aluminum engravings, I always use diamond bits since these give a great result and they are very durable. There are all kinds of different sizes but there are three basic bits that get you started in a good way. http://www.douruytool.com/cnc-end-mills/engaving-bits/