Eyeglass Frame Grips--Hinge Tighteners - 4mm Inside Diameter - Rubber hinged rings that provide flexible tension for a secure and comfortable fit. Simply slip a frame grip up each bow over the hinges. The resulting flexible tension will give a tight, comfortable fit. Pins and screws in these hinges cannot become loose or fall out. 10 rings in each package. Each ring is approximately 4mm inside diameter. Please measure your bows to make sure that these will fit.