Do you mean the hamster wouldn't penetrate through the cage? Sorry I'm just a bit confused, but it is possible that 3-4 cm is good, you could also use plexiglass as windows in the enclosure (there is another HC post that verifies that this is safe for hamsters). Here's the link to that conversation, you might find it useful because it talks about building cages:
Plexiglass vs glass, your opinion?. I'm just a bit confused on what you're asking but hopefully this helps!
Let me know it was something else you were confused about.