What brand of thread was it? If you can provide the brand, type, weight and ply of the thread, that would be very helpful. Some brands are better than others, plus weight and ply give an indication of thread strength.
How far apart were your quilting lines? The farther apart your quilting lines are, the more stress is put on the thread (from washing, drying, and using). I like to use 50wt 2-ply Aurifil for quilting on my domestic machine, but this is for fairly close quilting or for decorative stitches (such as the serpentine); it would probably not be strong enough if I did straight line quilting with lines 6 or 8" apart.
The fact that the thread broke on the hand-stitched binding indicates to me the thread was not strong enough. I have always used 50wt 3-ply thread (single strand) on bindings and never had it break.
Was this new thread? Old thread (and it possibly could be old coming off the shelf) can develop dry rot and break easily. If you still have the thread, take a strand between two hands and jerk them apart to see if you can break it that way. If you can, it's too weak.
I can't remember ever remember buying thread that said "machine quilting" on it. Curious about the brand.
Edit: Some people get away with using serger thread for piecing and quilting, but I suspect they piece with fairly small stitches and put their quilting lines in fairly close together. The weakness of serger thread is okay for serging because there are always a minimum of 3 threads working together for a serger stitch. It's not great for sewing on a domestic machine because of the weakness of the thread and also because it is made with such short strands of cotton (which makes for lots of fuzz and lint).
Last edited by Prism99; 01-04-2014 at 07:10 PM.