The hinge is the only moving part on an eyewear frame. The hinge helps keep the frame tight, takes the brunt of many impacts and allows the temples to fold in or out. Therefore, a high quality hinge will prolong the life of the frame.
A barrel hinge is one of the most popular hinges to feature on eyewear. A barrel hinge is the one with ‘loops’ and a screw through these loops. The ‘loops’ are the barrel. The amount of barrels usually depend on the thickness of the temples. The thicker the temple results in more barrels. This is to strengthen the hinge. Barrels typically come in intervals of either 3, 5 or 7. Some of the barrels are fixed to the temple and the others to the rear of the end pieces. The advantages of a hinge barrel are, added durability and a strong mechanism. The disadvantages are over time the hinge made become loose, rust and on some occasions the screw pop out of the mechanism.