kentdvm recently posted an Instructable for a carpenter bee trap, http://www.instructables.com/id/Making-Carpenter-Bee-Traps/
which uses two bottle caps connected together as part of the assembly. He used tape to connect the bottle caps, and here I offer another method that uses 1/2-inch metal grommets from a tarp repair kit. Photo is of one of my own variations of the trap, designed to fit under a small roof overhang. A separate Instructable for this trap will be posted soon.
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Step 1: Tarp Repair Kit
I happened to have a kit for replacing metal grommets in tarps, bought years ago from some mail order tool supply company. It contains 1/2-inch metal grommets and metal capture rings, a tool for punching a hole through the tarp, and two tools for easily and neatly setting the grommets.
Step 2: Punch Holes in Plastic Caps
The kit's punch made clean holes in the caps when pounded against a wood backup block. The holes need to be enlarged slightly by rattail file or sandpaper.
Step 3: Set Grommet Using Ball Peen Hammer
These green plastic caps are too thick to use the metal capture ring, so the grommet is set without one. These caps do not have an inner seal ring that needs to be removed. The tarp repair kit's setting tools will not fit into the caps, so the grommet is spread by tapping the ball of a ball peen hammer onto the metal using a second hammer. The backside of the grommet is supported by the flat end of a metal rod during the peening.
Step 4: Caps Connected Without Capture Ring
Two green plastic caps well connected without metal capture ring.
Step 5: Remove Seal Ring From Inside Blue Cap
Some caps have an inner seal ring that must be removed to reduce its thickness. The ring is most easily removed from this type of cap using a knife through the hole punched in the cap.
Step 6: Remove Seal Ring From Inside Clear Cap
The seal ring is most easily removed from this type of cap, whose plastic is very thin, before the hole is punched through it.
Step 7: Blue and Clear Caps Attached Using Capture Ring
The plastic in these two caps is thin enough, with their seal rings removed, that the metal capture ring can be used with the grommet. The grommet is again spread using the ball of a ball peen hammer, then somewhat flattened using a flat-ended metal rod tapped with a hammer.
Attaching the caps together using a metal grommet should provide a long-lasting connection in the carpenter bee trap application.