If the tool measures exactly 10.5" in one dimension, then you could use that dimension to measure and cut your 10.5" squares, but you probably already figured that out. I don't have the tool (and don't buy June Tailor products in general because of 2 bad experiences with them) but from looking at it on the amazon site I don't think that it would work in the way it is meant for marking the sewing lines all the way down the diagonal of the 10.5" square. You really don't need a special tool to do any of this anyway. Just use a "regular" ruler and you'll be just fine.