It's one of these simple contraptions that really help in the shop. I have many string winders, but this one is really useful to give that little turn to the tuner washers to secure them into place and avoid that possible wobbly source of tuning instability. Added bonus is, since this is not an actual wrench with a proper handle, and you will tighten the washers by rotating the tube between your fingers, you are guaranteed not to over-tighten.