I love that these little square beads measure exactly 1/4" long. So satisfying! We've been trying for a long time to find a way to use these vintage brass tubes on a necklace - no luck. But as geometric stud earrings, they work great. Posts and backs are sterling silver. "Air Gap" is a plumbing term, by the way - it refers to a pipe fitting of some sort. We imagine that they resemble these earrings.