Keepons are NOT one size fits all. Size concepts like small, medium, large aren't helpful in describing Keepons because for this product to work it must be threaded past your eyeglass temple tip (usually very wide) and unstretch itself to sit tightly around your temple bend area (usually very narrow). And since eyeglass manufacturers don't standardize temple tip widths and temple bend widths, no single style of Keepons will fit all styles of eyeglasses. Therefore to know which Keepons you need, you need to first know your own eyeglass temple tip width and temple bend width and then see which Keepons are compatible with your measurements. Our Keepons Fitting Guide takes you through the measurement process.