Scaly-breasted Lorikeets are on the smaller size of parrot species. They are smaller also (just a little) than Rainbow Lorikeets, and so prefer a slightly smaller nest box entrance to keep them safe from the competition of larger Rosellas and Rainbow Lorikeets.
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.