[Oldbikerider]

I'd also question why you'd need a metal coupler, because it's just connecting to the mating spline pattern on the gearbox output which is only made out of plastic. If you need to connect the coupler to another larger component you could bolt the coupler to an adaptor hub using the existing holes. That way you don't need to machine the complex spline pattern.

Team 3132 is using one of these couplers in our robot this year. It's modified by turning it down on a lathe and other parts are added to it. The plastic spline is a nice snug fit onto the gearbox output spline - it feels strong. And as pointed out above the plastic spline connection will be stronger than the worm and worm wheel in the gearbox.