15mm Square cats eye clasp. The measurement is of the square. In total the size with loops is 25mm. Clasps are jewellery fasteners that you can use to connect/end off your bracelets or necklaces. There are a huge variety of jewelry fasteners for different situations or just for different decorative purposes. Jewelry clasps are not just functional components used to securely connect two ends of a necklace or other piece of jewellery. The purely functional ones are there for function only, with a subdued appearance that keeps them from overpowering the jewellery. Others are bold, stunning, &/or decorative and are used in innovative way as part of the jewellery's integral design. When you are producing high-end jewelry with precious metals and more expensive beads, you will need clasps and fasteners that fit the top-end of the market. It is always unwise to expend good money for top-quality beads and then take the risk of using lower-end clasps which would detract from the final value and look of your finished piece. Some types of clasps are more secure than others and some are more difficult to open and close without help from another person. Below are selection of clasps with their accompanying descriptions.