If you want to attract bluebirds, you may as well use a pretty house.  This nesting box has a pretty blue roof and all the requirements for an excellent house.  Good ventilation, drainage, and an easy latch to turn and open the side for cleaning, It even has predrilled holes and you get two brass screws that won’t rust.  A pretty bluebird is etched on the front.  What more could a bluebird want?  The hole is 1 and 1/2 inches.  Which means it will also attract a Carolina Wren, chickadee, titmouse or nuthatch.  It’s whoever gets there first.