The hidden engineering that keeps your mechanical watch ticking for forty hours straight

Countries & Cities · Published 15 October 2026 Swipe more like this →

In short: A mainspring is a coiled metal ribbon that powers mechanical watches by storing energy as it tightens. While it seems simple, this device must deliver constant force to keep time accurate. Modern engineering has transformed these springs from fragile, breakable components into reliable, long-lasting power sources for your wrist.

The mainspring replaced weight-driven power in 15th-century European clocks, enabling the invention of portable timepieces. Early versions were made of untempered steel, requiring twice-daily winding. By 1600, these mechanisms had evolved into the first pocketwatches. Because a spring's torque naturally diminishes as it unwinds, early clockmakers struggled with accuracy. They experimented with complex solutions like the stackfreed—an eccentric cam—and the fusee, a cone-shaped pulley that adjusted mechanical advantage to even out the force.

The modern standard, the going barrel, was invented in 1760 by Jean-Antoine Lépine. It uses a longer spring coiled under tension, utilizing only the 'flat' section of its torque curve to provide consistent power. Today, these springs are crafted from advanced 'white metal' alloys, such as nickel, chromium, and cobalt. These materials are stainless, non-magnetic, and possess a high elastic limit, making the frequent breakages that plagued watchmakers until the 1960s rare. Such springs are typically 20 to 30 centimeters long and 0.05 to 0.2 millimeters thick.

Self-winding watches introduced in the 1950s added a slipping clutch, or bridle, to prevent overwinding. This device allows the spring to slip against the barrel wall once full tension is reached, protecting the mechanism from damage. Despite the myth that winding a watch fully causes 'overwinding' damage, timepieces are designed to handle this. If a watch stops while fully wound, it is usually due to dried oil, dirt, or a broken balance staff rather than the spring itself. Servicing remains essential, as springs can eventually become 'tired' or deformed, losing their ability to hold the necessary tension for a full 36 to 40-hour run.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Most watches now tick quartz; luxury still winds springs
• Before the wristwatch, the pocket watch was the ultimate tool for precision and status.
• The mechanical arms race to map the heavens on your wrist
• The physics of motion: how your movement powers a watch
• The mechanical heartbeat that turned fluid flow into precise, rhythmic timekeeping
• Majuli is the world's largest river island, but it may vanish within two decades.
• The Main River is a vital artery connecting the North Sea to the Black Sea.
• The Makah people have maintained their maritime traditions on the Pacific coast for millennia.
• The Soviet Union's most influential security arm: how the GUGB shaped state control
• Could this harsh salt desert be the cradle of modern human evolution?
• The University of Texas Tower: From Failed Library Automation to Iconic Campus Landmark
• The Malabar Muslims: An Ancient Indo-Islamic Synthesis Born from the Global Spice Trade

More in Bodies of water · More in Countries & Cities · Latest · A–Z · All topics