So, it was a relatively small task to make a threaded plug for the headstock oil top-up hole on my old Macson.
This has always been missing whatever the original threaded plug was and has had a plastic hydraulic blanking plug fitted at some point in the past.

I had the top off the headstock last week and determined this required a 9/16" BSF plug. I hadn't realised it was actually threaded until I cleaned it up and removed the perished rubber gunk from the threads. A replacement plug should be pretty easy he thought, machine and thread a piece of scrap aluminium out of the odds and ends box and knurl the end.....

First setback was no 9/16" BSF die - scope increased to include single-pointing the thread.
The second set-back was that all my threading inserts are 60 degrees and the only 55 degree one I have is a HSS one I made for the boring bar for internal threads - small scope increase to use the boring bar but because of the width of the knurled section that was done by doing the cutting in reverse with the boring bar tool being fed into the rear side of the job.
The third setback was setting the gearing up for 16TPI - my machine has a combination of change gears and a gearbox and 16 TPI requires the spindle and gearbox gear to be the same. The standard recommendation is 2 x 30T gears as there 2 x 30T in the standard set but of course my set of change gears only has one of each gear size.....

I have had good success with 3D printed change gears on my older lathe so for this one-off a plastic 30T gear was drawn up in Freecad, printed and fitted.
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The actual threading was very straight forward being a 1/2" thread in aluminium.
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Looks a little out of place on the Macson but it fits nicely and probably worth the messing around.
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