The HT-201 is an inexpensive IR camera module for your smartphone with fixed focus.
If you want to use it in near range, such as for locating hot spots on pcb boards the image is not very sharp. You can improve the sharpness and therefore resolution by adding an additional lens, such as a ZnSe lens with d=19mm and f=50,8mm which is available on eBay.
The lens holder is required for attaching that lens to the camera. If 19mm lenses are actually out of stock you could also take a 18mm or 20mm version. The FreeCad source is included and easy to modify for different lens diameters.
To avoid a mess of support material the holder is splitted into two parts which will get glued together with CA clue. Both parts are printed with TPU and 0.2mm layer height.
The author hasn't provided the model origin yet.