This tool securely holds the PTO shaft of an OS 21XM while you remove the nut from the shaft so that you can replace bearings. There is a hardened steel shaft that is pressed in place and aligns with the crankpin cut out on the PTO shaft. Once the PTO is secured with the included screws, you can now place this block in a small vise so you can loosen the captive nut on the PTO shaft and subsequently the bearings.
If you have ever tried to remove these PTO shaft nuts, you know that its a bear to hold the shaft from spinning. This makes it a breeze!