What kind of thread do I have?
 

I have a really big cone of cream colored thread that I bought as "quilting thread". I was too naive to ask if it is for hand- or machine-quilting. It is beautiful, not very fine, and I actually used it in my machine a little, but now I am not sure if I should have. Is there a way to determine what type of thread this is? I don't hand-quilt, but I don't want to waste it. If it is for hand quilting, do I have to clean up my tension discs?

I will be watching this thread - I have a big cone of thread that I picked up at a yard sale that I wonder exactly what it is :)

If it is labeled quilting thread then it is okay for the machine. If for hand quilting only it will be labeled for hand quilting. Most hand quilting thread will have a glaze on it making it stiffer then regular thread. If the label says quilting for machine or by hand then there is no glaze on it.

if there is no label and you are trying to determine the fiber content, wrap it several times around your fingers to get a small hank. Use tongs and work over the sink with a small bowl of water. Light it with a match, then extinguish. Poly or poly blend will melt leaving a hard bead or bump. Cotton will just produce ash.
Also, if you are not sure of how old it is, make sure you do a break test.

Quite a few of the larger cones of thread were/are for use with sergers or industrial sewing machines. Try the burn test as noted above.

I've had good luck using these larger cones on both my Janome machines - I just have to use a thread stand to hold the cone.

some cones have a label inside the cone(bottom).

I agree with the burn test suggested above. Of course, the other thing to consider is that sometimes even "quilting thread" can vary significantly in quality & it does cotton thread does go bad eventually with age. I had a few of those threads that I bought when I first started quilting. I was so proud of myself for buying "mercerized cotton" -- little did I know that was code for "low-quality thread that is made with short-staple fibers so the only thing we can brag about on the label is that it's mercerized". I donated 3 spools to my guild auction. A few people bid on it to use for basting their quilts so it didn't go to waste. Personally, I prefer brightly colored poly thread for basting, so I was glad that those spools of cotton thread could help benefit our guild fund.

I too have a super large spool of thread on a wooden cone, purchased from the local DAV....it's the strongest thread I've ever come across. Perhaps was used in an industry. I haven't used it on my machine, but if I need to hand gather something it's my go to spool.

I have one of those odd cones too, originally used for topstitching khaki pants, so its a bit heavy.

When you do the burn test, if you get both hard beads and ashes, you have a poly/cotton blend. You can also put a bit into bleach. If it disolves, it's wool.