This was the original military sight.
It's held on with a 4mm/70pitch screw - one of those weird ones with a wide flat head that requires a two-prong spanner to remove. I had to (very carefully) drill mine out.
I used a 4mm/70pitch screw from the hardware store to make a stud.
That fit in the old screw hole.
I bought a 1/2" x 20 threads per inch nut and a couple of bolts.
And modified the nut by drilling and tapping a 4mm/70pitch hole in one flat, and rounding it off, and thinning it.
Then modified the bolts to make the apertures.
Then screwed the nut onto the stud using an o-ring and nylon washer as spacers.
Then I blued the nut and apertures. Here it is before bluing. I've always intended to go back and make the apertures a little thinner, but never got around to it.
