Outdoor Pen, 1 1/2 inch square opening Yes kits can get out through this size hole but adults can't. I use it for indoor cages and its not to long before a kit can be put in one of these cages. The reason I use this "interlocking Grid Storage System" is that the pannels are 14 inches square and white electroplated paint (I don't like black or galvanized) and the cost is quite cheap. I got these at Sam's Club if anyones interested. [Posted in FML issue 3093]