Keepons eyewear retainers are famous for preventing eyeglass slipping. Though, a fitting is needed before buying this product. Specifically, you need to first know your own eyeglass temple bend diameter and temple tip diameter. Our Fitting Guide takes you through the measurement process and then suggests Keepons styles that are compatible with your measurements. You can do the fitting at home, you only need a ruler, and it takes about 3 minutes. To access our Keepons Fitting Guide, please follow the link between the brackets below. Once there, please CLICK ON THE HELP TAB in the middle of the page otherwise the guide won't be displayed. (https://www.amazon.com/sp?_encoding=UTF8&asin=B079KN87SC&isAmazonFulfilled=1&isCBA=&marketplaceID=ATVPDKIKX0DER&orderID=&seller=A2UB1M927IZI07&tab=&vasStoreID=)