If you are needing a little help calculating the shrinkage for your clay to fit the lids these shrinkage rulers are here to help. You give us the rate of shrinkage for the clay you use and we will ship a ruler out with your order based on that percent. These rulers are easy DIY but for those of you that need it done I have them available. They are simply laminated paper. When using these rulers ALWAY measure from the "zero" not the edge of laminate. The edge of the ruler each time to the line marked "linds" you should get a perfect fit every time! As long as you have your shrinkage % correct, and this number can always be found by the manufacturer of your clay. These rulers go up to 8" actual length.