This is a tungsten carbide tool used to mill isolation on a PCB. It is supplied with a stopper ring, allowing hassle-free tool change operations
As the tool has V shaped tip, the diameter is stated for the minimum and maximum width. The smaller of the tools (0.1-0.15mm) has 60º tip angle, while the larger one is 90º.
The shank measures 3.175 (1/8") in diameter.