I made a craftsman picture frame from 3/4" stock that is 13" X 21" to mount two 5" X 5" X 5/8" decorator tiles, separated by a rail, for the Warden. The stock is 3/4" QSWO. I cut the inset only about 1/2", leaving about 1/8" of each tile hanging out the rear of the frame. The tiles have some heft to them, probably weighing about 14 ounces each.
How can I secure the tiles to the inset? I don't want to permanently secure them with epoxy, I want some type of mechanical fastener. Since I am social distancing myself from my family, the frame will be mailed to her.