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The spread on the scales will vary a little bit with the length of the scales and the amount of taper the tang has. I would not put too much store in measuring that.

True, that works perfect for 1/2 hollow to wedges and fails on full and extra hollow blades. It is where I started, and you are correct that it may very well wind up at 1/2 that. It all works...

The taper of the wedge should match the taper of the tang. Typically I go with the wide end of the wedge id the same as the width of the tang at the pivot hole, plus if you are using thrust washers.