The combination shafter is a precision tool manufactured in Germany. The shafter can be adjusted for any shaft diameter. As a result, shafts with all three common diameters (5/16, 11/32, 23/64) can be compressed and exactly calibrated in the process. The wooden shaft is compressed to a precisely defined length and to a precisely specified diameter, and is now perfectly adapted to all parallel points (Bearpoints, TopHat etc.) Choose the diameter of shaft you need to compress, there are 3 choices 23/64", 11/32" and 5/16", just twist the dial until the little slot mark lines up in the window with the desired diameter. screw in one of the collars supplied, again there are the 3 main sizes.
You will notice a bar sticking out from the rear, this is to allow you to place the tool in a drill, then with the drill spinning the tool gently feed in the end of the shaft, it only takes second and your shaft will be compressed by the bearing inside the tool and leave you with a shaft with the end compressed to exactly the right diameter and exactly along the length that will fit inside the parallel point.