One thing which I think is just as important as diameter is the nature of the surface of the part of the pin in the wrest plank. Old pins were generally made from drawn wire which was often not quite round and had grooves because of the imperfect draw plates, modern zither pins are threaded. I think the advantage of pins with a 'distressed' surface is that they tend to turn more smoothly without jumping. I have used pins of diam. 1/8", 5/32". 4.5mm ,3/16" mostly made from hard bright mild steel in wrest planks of hard English beech. The all work more or less my preference is actually 3/16" although this is a bit bigger than  authentic . The only way I could get any pin to turn smoothly was to use graphite ( 6B pencil). In the future I plan to use a softer steel and modify the surface by filing as in the English tradition or squashing the pin slightly off round and of course a softer wrest plank such as red oak.

Richard

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