I asked this question elsewhere, relating to building a linear-pedal bicycle. The discussion ran towards the
Alenax Transbar bicycles, and the custom double-sided, double-drive rear hubs they used.
It was explained to me that the double-freewheel BMX hubs have the threads on the left side
reversed--because the point of them is to allow mounting two different freewheels and use the wheel as a flip-flop. If you try to use the left-side of a double-side hub as a left-side drive, it'll come unscrewed. --Or rather,,,,, the left-hand side freewheel on a double-sided hub only works right when it's on the
right-hand side. The left-hand side is not meant to be used as a left-hand side drive.
There are normal right-hand-only BMX hubs, and normal left-hand only hubs, and flip-flop hubs (that have right-hand freewheel threads on
both sides) but nobody knew of any hubs that were both double-sided
and opposite-threaded.
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