Wooden Mandrels - for wire wrapping, etc. Use to make large jump rings and to create curves and loops in wire jewelry designs. 'Ideal for Continuous Circle Aluminum wire jewelry projects.' No idea what that means - that's what the package says. You get 6, round, wooden mandrels in a travel/storage case - conveniently labeled for size. Sizes are 1/4, 3/8, 1/2, 5/8, 7/8, and 1 inch - which is 6.4, 9.5, 12.7, 15.9, 22.2, and 25.4 mm.