|I just made a pattern (Kwik Sew 2647) that used thread loops and buttons for closures at neckline and sleeves. The pattern directions didn't show how a thread loop is constructed, so in case anyone doesn't know how, I thought I'd put the technique here.
I generally make mine with several lengths of thread rather than something like buttonhole twist, since I never have anything like that around.
Thread a needle with about four lengths of thread. Make them perhaps 18 inches long when doubled. Knot, put through the fabric, loop around a short pencil or something approximately the diameter you are looking for, then pull back through the fabric. Move the needle perhaps an eighth of an inch to one side, and push it back through again. Now you have a loop, and the thread coming back out very close to one side of the loop. Move the needle through the thread loop, and then between the thread loop and the length of thread coming back out of the fabric. Gently pull taut while positioning it close to the fabric. Repeat. When all the loop is covered, push the needle back through the fabric and knot.