This is a very interesting case. There are rotary extrusion wheels made by a leading company with special and unusual pattern of round keys and keyholes. We have received a request to find out what is the cause behind the very specific way of defect of these wheels.  The cause that these wheels have to be removed and replaced usually is that from all of the 8 keyholes cracks start the same way and the cooling water leaks through this cracks.