"And he puzzled and puzzed, 'til his puzzler was sore . . . " (from "How the Grinch Stole Christmas")
I have puzzled over those clips for a long time. Have not had a "Eureka!" moment yet. Those things annoy me!
These thing do not annoy only you. They annoy me as well (still).
I wrote that I thought they were machine-made. Some say they have not.
They are made out of non-magnetic metal and have a silvery appearance. This excludes brass or copper, since exposure would have produced a layer of copper oxide which tends to be green(ish).
This almost only leaves aluminium.
The "clips" appear to me to be about 1.5 mm thick.
Small clips, 1.5 mm thick, aluminium, carefully hand-made. Screw is obviously a wood screw, meant to be screwed in wood at least 30 mm thick, since the screws are about 25 mm long.
30 mm is a thick plank for a box, but who says the screws were screwed into a plank ? Or something even thicker ?
Some will call me Captain Obvious now, I know.
Some of Tighar's members, I am sure, will have some (excellent) skills in working, transforming aluminium sheet.
Now, please get a piece of 1.5 mm Al sheet (Dural if you wish), and trace the outline the way a professional tracer would do it, using tracing blue or, nowadays, a felt marker and a tracing needle. Of course, you would have previously made an accurate sketch of the piece, traced it on cardboard or so and then cut it out to make your tracing pattern on the aluminium.
Place your traced piece of Al sheet in a vise with soft clamps, get your finest jigsaw to make a slightly too large rough cut, much in the way a jeweller would do it, and cut the "clip"out of the sheet.
Next step would be to "finish" the "clip", smoothing the edges with file and sandpaper so not to leave any saw burrs and drill the hole, again without any burrs.
Handmade, you say ? Maybe, but my guess is that you may well spend over one hour to fabricate one of these clips. An expensive "clip" in any time frame.
I happen to live near Angoulême, in the Charente department of France, a town with a world reputation of jewellery making. A "bijoutier" here, is a person, artisan who does all the "metalwork" before any precious stones are set in by another, specialized artisan.
So I went to see my friend "bijoutier" Stefan, who has his workshop in the village of Sers. He is known for precision, fast work. I showed him the pictures of the clips.
To reproduce those, he said, with the same precision, he thought he would spend about one hour apiece. He also thought the clips were stamped out, not being worth the work for whatever purpose they may have been meant.
So my point is: if the clips were really hand-made, some skilled person must have spent substantial time fabricating them, which might indicate they would have been used for some very valuable (wooden) assembly of some sort.
Just an Idea i had.
Rudolf.