[EricH]

The inside of the output gear on the FP transmission is an octagon. We just made some octagons of the appropriate size, put a hole for the shaft in, and added a keyway. (We also put hose clamps around the outside of the output to make sure it stays together.) Makes it really easy to put two of them together. Also can be adapted to any size of shaft that fits through the hole at that end of the gearbox.

This use can be seen here. Look at the base area of the mast and take a close look at the FP. The metal is an octogon with a shaft collar on this side of it.