This grill is a drop-in replacement for the rear engine bay exhaust ports on the model. All you have to do is cutout the flat area inside the port (don't cut the raised lip), and glue on top of the remaining lip.
Modelling is referenced from the VFX breakdown for "The Force Awakens".
These complement quite nicely the turbines already in my shop.
This item includes only one unit, so you'll need to order up to 6.