It is a lens aasembly that has the front IR cover, a plasric fresnel lens, a pinhole to set the focus and field of view and then the sensor. All the optics are assembled, then held for alignment with screws. After setting and verification of alignment the whole lot is painted with a glue and a solvent, to weld the plastic parts together into a single part so they do not drift or come loose with time or vibration. Screws are for preliminary alignment, the actual holding is with solvent welding on the lens tube itself, and with black rubber reinforced cyanacuralate glue on the actual laser diode holders and the lens alignment tube. That stuff will not let go, the plastic will always fail first, it is not possible to undo that. You can see the bloom from the glue and the remains of the accelerator used to get a fast cure on the parts.