Reducers are designed for round punchers.40/38- for a puncher labeled 40 mm for BioThane strap 38 mm40/25- for a puncher labeled 40 mm for BioThane strap 25 mm20/19- for a puncher labeled 20 mm for BioThane strap 19 mm20/16- for a puncher labeled 20 mm for BioThane strap 16 mmMaterial: PLA (polylactic acid)