This adapter enables to mount your external spool on top of the AMS, so that all of your spools are in one place.
I find it better than mounting it on top of the A1, as doing so shifts its center of mass higher up, resulting in amplified vibrations.

This adapter is printed in two parts and fixed with 4x Hexhead M2x20 Screws and 4x M2 Nuts.
I admit it takes a bit of fiddling around to mount it, but you can use the allen keys in the accessory box of the printer to screw the screws in.
Take the bigger one to hold the nuts in place and use the little one to screw the screws in (as shown in one of my pictures).
To facilitate the mounting i suggest removing the spools temporarily.