A multi-purpose setup jig - it can be used on wheels 150 - 250mm diameter, so as your grinder wheel wears down, it can be adjusted to re-calibrate to the correct angle. Allows you to setup the angle correctly on your wetstone grinder anywhere from 15 - 75º. As a side benefit, it contains angle checking grooves around the outside so you can check the angle of tool needing to be sharpened to improve setup times and accuracy.