A locking ear back, sometimes called a locking earring back, is a finding designed to secure a stud earring more positively than a conventional friction (push) back. The standard friction back relies on a small barrel containing a coiled spring or a deformed piece of metal that grips the earring post by friction. It is adequate for most light wear but not reliable for valuable studs, which can work loose during normal activity and disappear without warning. Locking backs address this risk through a positive mechanical engagement that resists removal until deliberately released.

Common designs

Several locking-back designs are in production:

• Thread-back (screw-back) earrings, in which the post is threaded and the back screws onto it. The thread is typically machined to a fine pitch (often 0.4 mm), and the back includes a knurled grip to allow the wearer to spin it on. The design originated in the early twentieth century and remains the standard for high-value diamond studs sold by major retailers including Tiffany & Co., De Beers and Cartier. The drawback is the time required to put on or remove the earring, and the risk of cross-threading by impatient users, which can damage the post.
• La Pousette and similar lever backs (named after the French firm that developed the original design), in which a small lever on the back pushes a tiny gate clear of the post when depressed. Releasing the lever closes the gate against a notch on the post. The design is fast and secure but more visible than a flat friction back, and the spring can fatigue over time.
• Alpha back, a brand name for a flat locking back that uses two internal levers gripping a notched post. Alpha backs are popular for medium-value studs because they are slimmer than screw-backs and faster to use.
• Disc-back or guardian back, a wide flat disc that slides onto a friction back to provide additional bearing surface against the back of the ear and reduce the risk of the friction barrel sliding off. These are sometimes used in combination with a friction back rather than as a standalone solution.

Trade context

For diamond studs above one carat per ear, the trade convention is to fit screw-back posts. Most insurers issuing standalone earring floaters will require evidence of a positive locking mechanism for high-value stones, and several decline to insure stones above two carats per ear without documented screw-backs or equivalent.

Retailers selling expensive studs sometimes upgrade backs as part of the sale. A diamond stud purchased with a friction back can be retrofitted at most jewellers; the post is unthreaded, replaced with a threaded post, and a screw-back is fitted. The work is straightforward for an experienced bench jeweller and typically costs a small fraction of the stud's value.

Failure modes

Even locking backs fail, and the failures are instructive. Screw-backs fail when threads strip from cross-threading or from years of soft-wear that allows fine debris to grind the threads. Lever backs fail when springs fatigue. Friction backs fail when the spring or grip mechanism loses tension. The recommended practice is to inspect ear backs annually on valuable studs and to replace components that show wear, much as one would inspect a prong setting.