This is a rough copy of the standard wheel pommel used on Rawlings synthetic sparring swords. The measurements are approximate, and I haven't printed it, so you're on your own. But if all goes well, you should be able to glue an M8 nut into the hole at the bottom and screw it onto your sword. I included a tolerance of 0.1mm for the nut, which you can adjust by changing the variable.
I've added the variable captive_nut, which when set to 1 will give you a hexagonal hole in the base to hold a nut. If you set it to anything else, you'll just get a plain screw hole so you can screw directly into the plastic if you'd rather. You may need to drill out the hole a bit to fit. Additionally, the nut_tolerance variable is now just called tolerance, and it applies to the screw hole as well.
I've also added a facet variable ($fn) to make the pommel more round, but consider changing this to get interesting polygonal pommels. Note, however, that this will also affect the base, which will not quite line up with the grip if it's not round. I haven't decided if I should force it to be round.
Also this is literally the second SCAD object I've ever created, so sorry it's a bit messy. I'm still getting the hang of this.