OK, you guys are probably going to get quite a laugh out of this, but here goes.
While wandering the aisles at a local big box store, I came upon some dog tie-out stakes. The kind that screws into the ground. I noticed the screw part was just about golf ball sized. I spent $1.19 for one. I took it home and cut off the screw (in-ground) portion of the tie-out stake. I found that a 7/8 inch dowel could be inserted ever so tightly and securely into the end of it, made even more secure with a generous but neatly applied helping of epoxy. Next, I reduced the diameter of the coil (screw) using a grinder. I would grind, try it in the golf ball bore of my barell, then grind some more. After about an hour's work grinding, I had a functioning worm, even if was only a single helix instead of a double. Spent some time making it look nicer with stain, varnish and paint. Like I said, I'm sure you are getting a good laugh out of this but it works.
Since then , I bought a couple nice duble coil worm heads from Dominick, but I still use my homemade (and cheap) semi worm.