The adapter is a 3D printed part to add an (optional) color filter and a diffusor cap to the Fenix LR40R. You can glue everything together and put the adapter on the Fenix on demand with a bit of pressure. An indentation in the adapter keeps the ideal position of the adapter. Some openings help heat dissipation.
And I don't need glue at all. Tolerances are so good that everything holds together well without...
Disclaimer: First FreeCAD project, last CAD experience (Solid Edge) now some years in the past... I remember that there was an easy way for hole patterns...