Samuel, it's a pain finding what the thread actually is, you can get the number of the spool then use I think gutermann's site to get the actual mara/tera of that product number, which I think I did as I was learning what Roger notes, it's not as simple as it sounds. The pain of discovering what the thread weight and type actually is why now if I buy, I'll only buy it if the vendor states that information explicitly. My assumption now is that if the vendor doesn't list it, or if the spool doesn't show it explicitly, I wont' buy it, unless I want the thin stuff. I actually don't enjoy doing this type of research, it's expensive and not really that fun, not to mention time consuming and materials wasting, so once I found something that seemed to be pretty good, I said to myself, that's fine for now.
I believe all the normal fabric store, and other 110/200 yd sizes, that's small and medium regular type spools, are the thin kind, except for one style that is heavy, but not as nice as the tera. Given that they cost around $2 for 110 yards, it's not really worth buying them compared to the big spools, on any project of any size, a backpack, a tent, you're probably going to use a big spool or so, give or take, especially with redoes.
You can also just compare them to the stuff diy/owfinc sells, which I also did. I actually noticed initially only by accident, because I first was using the fabric store guterman stuff, and was fairly easily able to thread 10 needles, even 9 with some effort. It's much harder to get those threaded with the heavier versions.
You're right that some fabric stores might have good stuff, but none I checked did, not small ones, not joannes, and not the local outdoor gear repair shop.
The big gutermann spools, 450-800 yds, show on the spool what it is, so if you can find those, you're set. Like, Tera 60, Mara 70 (I'm reading that off the ones I got from diygearsupply/owfinc), says on the top plastic of the tube it is rolled around.
I've bought the more consumer style in various roll sizes and all were the thinner version, that's 110yd, 200yd sizes I think.
For people wanting to check this stuff out, it's a cheap thing, just add on each of the tera sizes from diygearsupply, that's 3, and all of the mara colors, I think that's 3 as well right now, they cost like 3.65 each, then you can see the difference for far less than I spent on threads I will never use. I should sell that bag of too thick or not qood quality stuff on gear sales for 12 bucks or something, maybe someone wants it.
Oh I remember the bad brand, coats and clark, that's the one. Don't get it, it is not very good, and it costs the same or more, and for far smaller spools, than what diygearsupply offers.
the gutermann misspelling comes from actually knowing german, it's because I pronounce it in my head as gutter man, when of course, it's actually gooter man in german, sort of, so I spell what's in my head, not the actual word, lazy.
I tried going to all our local fabric stores, wanting to shop local and all that, and they just don't care about the myog market at all from what I can see, it's not something that even creates a blip on their financial radar, so they cater to their main market, clothes, cute embroidery done with those overpriced computer controlled sewing machines, craft projects, fashion dress makers, etc.