I believe this "Original Hard Shell Nymph Thread" is what used to be sold under the trade name "NYMO". It was designed to be used as a body thread for midges and you would wrap the body in bands of colors, black, grey or brown with white bands and then coat it with nail polish and it would dissolve on the hook, leaving a hard shell segmented appearing body behind.
We used this on a series of very simple dry flies that were tail, thread body, hackle tip wings and hackle only then coated the body and the same thing would happen. It made a GREAT looking mosquito with black and white, and we also made the bodies out of olive, brown, grey, black and plain white. The patterns cast a very slender shadow and were pretty productive.
It used to be spooled on normal thread bobbins and sold at fly shops in the 60s and 70s and then it disappeared, but the product is still available as a beading thread on odd shaped little spools of small volume in a variety of colors. I saw it about 4-5 years ago for the first time in ages, but didn't buy it to confirm it still had the same properties. (I still have about 10 spools of the original stuff)
---------- Post added at 09:44 AM ---------- Previous post was at 09:33 AM ----------
Thanks Silver Creek-
Some great info here. Yep, it was apparent that they weren't the same, but in days of yore, when thread was Champion Silk and Black or White, it was all the same diameter... mainly because it was originally used by physicians and surgeons for stitches!
Aside from those, there was always Pearsalls but I don't recall it having a diameter rating and it was in rather limited availability in the States (except the Northeast) and there was Danvilles which came in numeric and alpha ratings.
Too bad AFTMA standards aren't applied to leader/tippet sizes (they SHOULD be because they apply to lines!) and thread as well- if not AFTMA, some other standards body for sizing of thread or materials. Sewing Secrets: Confused by Thread sizes?
As for hooks (and beads) we will be left with that horrible legacy forever... even within a given package, you won't always have uniform sizing or shapes or shank lengths.
---------- Post added at 09:55 AM ---------- Previous post was at 09:44 AM ----------
Oh and ODDLY ENOUGH, it turns out there ARE both Federal and Military specs for yarn and thread!! Federal Supply Code (FSC): 8310 1/1