Very good metalwork there. It's difficult to know the exact size of some of the parts however you say that it is too hard to make the wing nut in this scale. Have you tried the simple method using an aluminium tube section crimped round the bolt, the wings can then be filed to shape. The photo shows a crude version I tried with a 2mm threaded rod, took around 5 minutes, with your skills you could make a better job.
Jim