The Troyer bluebird box, commonly called the slot box, is constructed from 3/4 inch weather resistant cedar with zinc plated hardware for durability. Opens for easy monitoring and cleaning. Considered sparrow resistant research does show it is rarely used by house sparrows. Approved by the North American Bluebird Society this box is a must for any bluebird trails. Mounts on any 1/2 inch O/D pole or order the BB-POLE for quick and easy installation.