I make mine from 7075 or 2024. The 2024 is aircraft grade and has a little more copper in it which makes it stronger but it dulls a bit over time. The 7075 is the highest in strength and aircraft grade asdo and is stronger than the 2024 which is stronger than 6061. I have found that the 6061 doesn't hold threads as well and I have stripped the threads on hubs I have made from it. Not often but once is too much. I would go to some of the smaller job shops in your area and they will sell or give you their cutoffs or bar ends. Here is a sketch I found on RCU. This one is just threaded with no mating taper. I cut tapers on mine as I feel you get a good mating between the parts. On a smaller engine you can do it without a taper but on a larger engine I wouldn't trust it. Just imagine the way the hub would look on the sketch with a taper and you can see the benefits.