Solid carbide end mill for metal cutting. Bits come in different sizes. I tried a 5/8" end mill with a 5/8" (8mm) shank. End mill, rectangular, 4 cutting edges. The drill is carbide. I find this end mill works well with my CNC router. Shaft size is metric, approximate size is inches. The bit is fairly strong and will cut through steel as advertised provided your CNC machine is up to the task. Overall a good choice for a solid carbide end mill.