The file 'Lens Centering Ring For 40W Laser Cutter / Engraver 3D Printer Model' is (STL) file type, size is 59.7KB.
I have a generic-cheap-ebay-40W-laser-cutter (sometimes called DC-K40) and the lens is smaller than its holder, making it lying off-center and sometmes at an angle.
This is the solution!
Lens_ring.STL | 191.1KB |