As Quora User stated in his answer, anything a hamster's head can fit through, they can get their body through. What does this mean to you? It means a smaller species like Roborovski hamsters can fit through incredibly small spaces. read more
I once read that if you can fit a pencil through the hole, a Robo can get through it. Same for mice, by the way. The larger hamsters need a little more space, certainly, but not as much as you might think. read more