We have a couple of adult females who can fit through 1 square inch.  1.5
would be a breeze for them.  If you have larger ferrets, go for it--but
folks with smallish jills, go with 1 inch or .5 inch square mesh.  We
caught Gibber going through the holes in the baby gate, which were 1.5 x 1
inches, and oval.  (Baby gate has now been replaced and the new one is
covered with sheet metal.)
 
Also, as far as rabbits and ferrets are concerned, I personally would
probably not combine them, simply because, to a ferret, a rabbit smells
like food.  As do mice and birds.  It's the same for cats; my cats have
never been trained to hunt, but they sure do know that my birds are food.
 
Some people have made the rabbit/ferret thing work, especially if they had
a VERY laid-back ferret and a largish bunny.  I also know some folks who
have a rabbit that freaks out if they come near him after handling the
ferts--instinctive fear of their scent.
 
Only in our living rooms would two animals like rabbits and ferrets be
friends.
 
Jen (whose ferret Gibber once went to sleep with a mouse.)
 
Jen
[Posted in FML issue 3094]