Our WPI Tool is a handy device for all fiber artists who want to measure their fiber's "wraps-per-inch". Two yarns that have the same WPI can be exchanged. This is important if you are trying to substitute one yarn for another for a given pattern. The WPI Tool is made from birch hardwood and measures 5" in length x 5/16" diameter. There are markings for up to 3 inches which allows you to calculate a more accurate average WPI on certain hairy yarns. There are also 1/2 inch marks. All markings are laser etched into the wood and will not wear off.