These are a bit hard for ME to describe. My eyes kinda 'glazed over' as Alan was explaining them. The fixture with the gears on it was just a fixture to show how the helical gears work as a set. The other fixtures are to hold the gear blank so the helical teeth can be machined with a profile single point cutter in a lathe. They hold the blank at such an angle that the tooth actually is a section of a circle. There is a 30 degree fixture and a 60 degree for the other gear. I wish I understood it better. Keep watch in Model Engine Builder magazine. There will be an article in the next issue by Alan, accompanied by an Excel spreadsheet.