This is considered an "optional accessory" for the 55-2700 kit because it does not come with the Panther 55-2700 kit, the kit comes with spherical rod ends that would be considered "fixed".
It can be used with the Panther 55-2700 if you want a quick disconnect option.
This Stainless Steel Quick Disconnect fits a rod that is 1/2in- 20.
This Quick Disconnect will fit on the 552700, 552900 or the ½” threaded rod 9902704