I had to Google "Hirth coupling", I didn't even know such a thing existed! It was an idea I came up with, thinking of poker chips, and how their edges engage, and I made my own. VERY time consuming but can be done using a rotary table and milling machine. The teeth need to be smaller to get less than 6 degree increments, but life is too short to make that many cuts. It take the same amount of time to make 2" as it does 4" and they take me 4 days to make a set so there isn't much of a market. Heli-bars has come out with something that may do the same thing and be more adjustable.
