We've got several 10" steel corner and line posts around the ranch here. Not sure how old but I'd say they've been in the ground for 20+ years. All these posts had "caps" welded on the top. They've got a very sloppy hole cut in the side that a 2 1/2" pipe brace goes in. Nearest I can figure they must be perfect for bees cuz prolly 50% have hives built in em. The bees get inside the 10" pipe via the sloppy cut hole in the side that may have a 1/2" to 1" gap around the 2 1/2" pipe.