Sweater Strings by Apple Yarns - a great notion that makes it easier to try on sweaters so you can check the sizing. 

What's included: A total of 3 cords, 2 -1 meter (40") Sweater Strings and 1 2.5 meter (100") Sweater String in a handy, screw-top storage tin.

These flexible silicone hollow cords are perfect for trying on your knitting without removing any of it from your needles!

The end of the cord squeezes onto the tip of the needles up to size 10. After it's attached simply slide stitches onto the flexible tubing so you can try your sweater on. When you are done, push all of the stitches back onto the needle and pull off the tubing.