As previously stated, this endwall is designed specifically for use with the Hercules 18 x 20 model canopy. This white endwall features a middle zipper to make entry and exit from the shelter simple, even if you've enclosed the rest with solid sidewalls (which must be purchased separately). The hook-and-loop fasteners that are included with this model work perfectly with those separately purchased sidewalls with flaps to really help close almost all of the gaps around the corner leg.
So a little addition after the purchase doesn't mean that you don't love your Hercules shelter. It just means that you, like many people, want every outdoor experience to be perfect. If you're looking to reach that perfect state by adding some additional covering to the outside of the existing structure, the King Canopy White Endwall with Zipper for Hercules 18 x 20 Model Canopies could be the perfect choice.