Size (Snap Hook) Overall Length: 40mm (height) x 24mm (width) Inner Diameter: 8mm (height) x 20mm (width) Wire Diameter: 2mm The included backpack buckle is the right size to be used in combination with the snap hook. It's sized to allow a 20mm wide strap to pass through. Since the snap hook and backpack buckle are a set, you can create an adjustable shoulder strap. I will be listing unused materials little by little (*´-`) I will be selling them for less than the price I bought them for, so please consider them☆ Bundle discounts are also available. Please feel free to contact me. Although it is a new, unused item, Please purchase it if you understand that it has been stored at home☆