I think there are more ways than any of us can think of for making joints. I would point out here the C/V joint has been around for a long time & since the advent of the Mini in 1959 they have been the go to joint in various forms, & we should ask ourselves why. I like many of tha ideas discussed here, but for $20.00 & about 1/2 an hour of my time I can have a true C/V joint that will adapt to most motors & shafts & I am sure has been well tested in competition by its makers who are one of the leading companies in the model car racing business & are very successful at it. I can see good & bad in the hex drive for instance, you are assuming that the head of a nut or bolt is a true hex. Those of us that use nuts & bolts everyday of our lives are well aware that is not the case. Can you imagine a drive made from an Allen screw turning @ 6000rpm and does not run true. In the case of my own prototype it was only out about 3 degrees and the vibration was bad,putting it mildly. The Dumas dog bone seems like good bet of all the ones you guys have discussed, but until something better than the HPI racing unit comes along, guess what will be fitted to my boats, Mick B.