the only thing for masons I bought was my block. When I got my first hive I had planted a lot of wildflowers for the bees, and I was admiring my bees in the wildflowers in April or May and saw a blue bee. I called the gal I bought the hive from and told her I thought I had a defective bee. She laughed and told me to run a search on blue bees. I have leaf cutters and a lot of small wild bees around here, have not yet had a successful nesting block event, didn't get the block in the refrigerator soon enough in fall of 2014 and found that they had hatched trapped inside the nylon stocking in my garage, just a couple of bees. and then something got my cells last year, hoping to do better in 2016. the woodpecker holes in the woods by the creek and the ones in my elm tree are probably well occupied.