Crown Bees Mason Bee Holes, Guard Tube and Insert 100% recyclable paper with no damaging plastic that retains moisture Innovative end cap viewing hole to identify used tubes Guard tube is perfect size for nesting mason bees with inside diameter of 5/16" (8mm) and 6" length 6-1/8" glassine insert fits snuggly inside guard tube with extra length for easy removal Each order contains 36 guard tubes and inserts