There is a lot of different types of mirrors for our lasers.
Some better than others, and some you will not see any difference on the K40.

Si Mirror

Silicon Glass Gold Coated. Good reflective index for our machines (less than 50w)
High reflective index, needs cleaning more often.

Cu Mirror

Copper mirror, better than MO, a bit below SI when talking about reflective index

Mo Mirror

Molybdenum mirror. Can withstand alot of “abuse” but have less reflective index than the SI-mirrors.
Good for up to 100w+ lasers.

K9 Mirror

This is the worst mirror you can ever put in your machine. Bad reflective index and really easy to damage with dust or mishandling. We do not carry theese types of lenses.
Theese K9 is often mounted in the K40 on delivery.

Aliexpress advertising