Charlie's Shed - repairing hexagons

Some while back I made a set of new chain adjusters for the Model A - the post is here. It took a while and wasn't particularly tidy - I made the screws on the lathe, built the heads up with weld and milled the small hexagons. 

This post is about fixing a similar issue. 

I was adjusting the rear chain on the W/NG one day, puzzling for the umpteenth time about the hex size which didn't fit anything other than an 8 mm spanner, when I realised the hex heads had been filed to suit  spanners that would have been available in Italy where the bike had spent most of it's life.

I resolved to fix them, and came up with a better way of doing it than the last time. Here's the problem:

I took the adjusters off and removed the paint so that I could hold them in a 8 mm collet.

I turned off the remains of the hexagon, leaving a diameter of 1/4":

I put a 1/4" BSF thread on the end, to suit some reduced hex nuts I found on eBay:

I added an undercut, so the nut, chamfered on one side only, would snug down to a square shoulder:

I brazed the nuts in place, not wishing to risk damaging the small hex with weld:

I cleaned them up on the wire wheel, and they look as though they have been there for years:

That took about an hour, with a much simpler set up than last time.

The only difficulty I found was obtaining nuts with that size hex - I can't find bar stock in that size - the smallest I can get is 0.445", which is for 1/4" BSF or CEI, or 3/16" BSW. It occurred to me that a simple way to machine a small hexagon bar to make nuts in the future would be to start with a larger one (could be metric or anything), hold it in a milling vice and reduce it with an end mill, using the larger hexagon to orient each face while I machined it smaller.