I went to a class in which I was told to cut some pieces 3 3/8 inches. I asked if it would be OK if I cut them 3 1/2 inches. I was told by the instructor (and several of the students) No, they need to be 3 3/8. After I had the blocks done, I soooo wished I had had that little extra on there. I have since made another like that, and the extra 1/8 inch made a big difference in being able to square up the block. Sometimes we have to go with our gut.