Treecreepers are shy little bush birds that walk up tree trunks, just like you walk along the ground. They are very vulnerable to predation by larger carnivorous birds and arboreal mammals, and so need a nest box with a small 50mm entrance diameter to keep them safe.
Here is a diagram with nest box key design features.
Here is some info on the different materials to use, or not to use when making your nest box.
