This is a Clark’s Dubbing Block. The original was found in Pete Hidy’s book about Flymphs many years ago. Pete popularized the block and made many and sold or gave them to friends. The block has a scale and is about 4 by 2” . This is used to make Dubbing ropes. To use you put on your knee. Lay thread around nail, lock in place in slit, insert dubbing and roll. Completed ropes are added to cards.