Yeah, should've made it clear I was only talking about deltas
Why do I ask? We have a brox compact with a nadgered rear axle (a short length of it was hexagonal section but is beginning to round off, causing sprocket to slip under load). Either we have to find a workshop that can rebuild it as it was, or, if there is a maker of trikes that is still producing something else that does the same job, we rebuild it and adapt it to their design and so we have a source of spare parts for the next time it breaks.
But from what Hilldodger says that may not be as simple as I'd hoped.