If you are just making quilts for yourself then you don't have to worry if 1/4" is exact. As long as you do them all alike it will work out in the end. If you are doing blocks to trade then you will have to make sure it is 1/4". I used tape and credit card like Bonnie Hunter suggests and I have top load bobbin. I have to remove and replace to put in bobbin but I have to check each time to make sure I put it back exactly right.