Maximum power available from an infinite source with specified dimensions.?

@Domenic - Please, the infinite source is clearly fantastic. The question hinges on how much torque could be transmitted by a six-inch square shaft with a coupling depth of six inches, given the known properties of realistic materials and stipulating that the shaft itself is not the limiting factor. It's an engineering question, not a scientific one.

@oillfieldtrash - Obviously such a source doesn't exist, except in a book of fantastic satire (or satirical fantasy) written by Terry Pratchett. It's an artifact of untold age and its existence is simply a given. But to get any use out of it the present inhabitants would have to couple to it using available technology, which is pre-steam. They have iron and steel. The thing is that since the device consists of a pair of six-inch cubes, the available surface to couple to is quite small and therefor the amount of torque that can be exerted is severely limited by the strength of available materials. So how strong can you make a six-inch square hole six inches deep? My hunch is that the maximum power you could get back then might be a few hundred horsepower, and even that might be way high because of how slowly the thing is turning. The fact that it *is* turning and cannot be stopped is another complication of course, but that way lies madness. Does that help?