1/4-26 un? why?

[mark]

I took the starter apart to freshen it up... prior to cranking/starting a 100E engine that has been sitting 3 decades. The brass stud had some burn/melted marks on it, (from jumper cables)...making it hard to get its brass nut off. So I mic'd the dia (1/4") and I could tell it was a fine thread...thus...I got out my 1/4-28 die. It threaded on easily the thickness of the die and stopped. So I took a wrench and wrenched it. By halfway, I noticed too many brass chips are appearing. My first thought was how did it cross thread! It screwed on easily by hand the thickness of the die!
Further investigating reveals it is a 1/4-26. Has anyone ever heard of a 1/4-26?
Looking at the pics, the left half of the stud is not touched. The right half is my 1/4-28 die work. I stopped the die half way and you can see the threads buggered up a little in the middle at the transition point.
27 TPI doesn't line up, 28 is even worse. But the 26 TPI lines up.
So I guess I will use a 1/4-28 nut and use washer to fill in the center transition. The 1/4-28 nut is now a little loose, so I might make a double thick nut to help keep from stripping the fragile stud threads.
Anyone ever pick up on this anomaly while working on their starter?

27.jpg (202.25 KiB) Viewed 6 times

26.jpg (132.84 KiB) Viewed 6 times

[mark]

I just googled it and according to wiki, it is a British Standard Brass thread. I wont explain it here, you can go to wiki to read it, but apparently they used 26 TPI for 1/8" to 2" brass diameters.

https://en.wikipedia.org/wiki/British_Standard_Brass