Mouse rack/cage, how much gap between the wires?

Ok, so I'm going to be building a mouse rack in the next few days/weeks, and need some advice on the wire to use. Do I need 1/3" or will 1/2" work? What's the largest size mesh you'd be comfortable with?

I use 1/4" on my mice and ASF racks. The adults will do fine on 1/2" but the babies can get through it. I can't find the 1/3" to know if that would work or not.

1/3 is the largest you should use as Sean stated with the 1/2 the mice will squeeze through and escape.