[Dick Linn]

Take a piece of appropriately sized aluminum tubing or bushing. Taper the end of a scrap of hex stock slightly, lube it and pound it through the aluminum tube, thus forming a hex. Spin it and use a file to turn down the outside until it is round and fits the bearing of your choice. Of course, that means using a bearing of sufficiently large size to leave enough material at the points of your homemade custom-forged hex adapter so it stays together. You could probably get it done with a wood lathe or drill press.