K40 Adapter for mirror 1 of Cloudray CO2 Laser Head Set, directly mounted before the laser tube, see here:
https://www.amazon.de/gp/product/B07P1YLR2T/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1
My K40 is a newer one, the holes in the standard mount for mirror 1 are 48mm apart. You must remove this holder and the set's replacement holder, but you should reuse the screws.
The author hasn't provided the model origin yet.