This set of 12 Class 15 threaded bobbins can be used in SINGER® and other manufacturer’s sewing machines. The pack contains 6 black-threaded bobbins, with 50 yards of thread in each, and 6 white threaded bobbins, with 50 yards of thread in each. The reels come in a reusable plastic case. All thread is 100% spun polyester. Consult your machine’s manual to ensure correct bobbin size. Never add thread to a partially wound bobbin, as it may be uneven and cause thread to tangle or break.