This book binding corner tool is an extremely useful cutting guide. Use it to cut perfectly mitered corners on the book cover, essential for creating professional looking finished books. The corner tool is made from very durable poly carbonate plastic. It is transparent, so the tool doesn’t get in the way of being able to see the project. It also has two sets of alignment notches on the two short sides. These markings assist with accurately positioning the cover material on the book case. One set of alignment notches correspond with covers that have a 1/2” wrap around, while the other set is for a 3/4” wrap around.