Trevor
Not sure where you get the 11/16 from apart from the end radii. As mentioned before the inside measurements of the slot are .069" (1.8mm) x .024"(.6mm) and the thickness of the end of the arm nearest to the slot is .024" (.6mm) thick, all very tiny.
Ian
Thank you for the explanation but, and apologies for saying this but, I didn't quite understand
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I did think about joining two pieces along their length but after several attempts at trying to form half a slot, I gave up with that one. I did think of another way of laminating by making a sort of elongated sandwich without the filling, the lack of the filling would eventually be the slot but, I gave up on that because of the tiny pieces and holding them all together while it was soldered. Also, the line of soft solder would be visible when it was blackened. My latest thought is to make up the bar as a single piece of nickel 20/24 thou thick with the plunger as part of the bar, a little down stand. This would do away with the need for a slot and I'm hoping that when it is held in the clevis and sat in the top of the little brass piece which has a dimple formed into the top of it that that would be enough to hold it steady. Nickel because I don't intend to paint this item and if it is heated, when cooled, it takes on a good weathered steel colour.
Jon