Bluebird Box House Woodworker's Vise The kit is extremely easy Size:100 Piece The kit is extremely easy to install and simple to use and maintain recessed top ring and large bottom ring for extra safety and stability Durable rust free galvanized wire meshPredator guard extends entrance hole to protect against predatorsPredator guard entry hole has a diameter of 1 1 2" Predator guard with an entry hole 1 9 16" in diameter for Western bluebirds can be purchased separately on the Replacement Parts page and retrofit to the bluebird houseBluebird house body has an entry hole with a diameter of 1 9 16" to allow it to be used for both types of bluebirdsFledgling kerfs provide extra grip for fledglings to climb out Tree Swallows