Many people think that the couplers are meant to break so they can
protect the rest of the machine or a circuit breaker. That is just
plain silly, simply because the prongs of the coupler are too tough to
break under the various scenarios that the gearcase would lock up. And
they don't break because of overloading the machine either. Here's the
truth: the prongs break because they are made of plastic, and plastic
can break over time.

The coupler with the metal sleeve is the standard part available on the
market today. The commercial-grade coupler with the reinforced rubber
piece is also available, but it is a mystery as to where this part ends
up. I have never installed it on a machine, nor have I ever seen it
already installed. It is debatable if this commercial-grade coupler
will last longer in normal operation.