you also need to know if the machine you are going to use for ruler work is a high shank or a low shank. The high shanks use the the same thicker rulers that long arm quilters use (I think they are 1/4 inch thick) The low shank machines would require rulers made for those machines as the foot and ankle get in the way of the regular 1/4 inch thick rulers and you can't place the ruler on all sides of a low shank foot. I think the low shank rulers are about 3/8 of an inch thick. But you don't want to use the low shank rulers on a regular long arm or high shank foot as they would be easier to get under the foot and cause damage.