Hey guys. I bought a drill to plant CRP. Looks like it's a Canadian u it and has a grass box on the rear. It is a 14x7 double disk drill. The prior owner (I assume) removed 2 disks. I'm wondering how these get put back on. On the outside of the disk there is a hex head which I thought was how the disk was installed on the casting, but its only a plug. Looks like it keeps dirt and grease out. The other side has a round shaft with a groove around it. Any idea how these are installed? Am I missing