For those who have the XL model,the coupling plate is placed underneath the ball to keep locking nut of the XL flush with the coupler for added protection.
The plate keeps the locking nut of the XL flush with the coupler, which in turn reduces the possibility of damage on the coupler should the XL pivot due to excess horizontal force. Install the plate by placing it under the ball before threading the ball into the cradle on the XL. The lip of the plate must face the back of the coupler.
This coupling plate comes included with your Trailer Valet XL purchase.