When I finished quilting the quilt shown here and turned it to see the back, the first thing my husband said was "My word, you must have used $50 worth of thread in that"!
I, too, was amazed at how much thread went into the quilting of this quilt. The cone on the right in this picture is brand new and the cone on the left is the one I just took off my HQ16 after quilting that Irish Chain quilt. The label says that there are 3,280 yards of thread on the cone when it's new. From the looks of things, I don't think I could quilt another quilt like this with just the remaining thread (it will be a long time anyway before I quilt another one that big, so I won't worry).
The thread that I mainly use in my HQ16 comes from Superior Threads. If I need a solid color, I use So Fine and if I need something more interesting, I use the variegated Rainbows. Their Bottom Line thread is great in the bobbin.
Yes, the thread from Superior is a bit pricey, but I believe that you generally get what you pay for.
4 hours ago