Screw-down crown

A screw-down crown has a threaded tube fitted to the case and a matching internal thread in the crown, so that it can be wound down against a gasket and locked shut. Compressing the seal this way makes a far better barrier than a push-fit crown, and it stops the crown being pulled out accidentally. It is standard on dive watches and usual on watches rated to 100 meters and above.

How it is built

The threaded part on the case is a tube, a short metal collar fixed permanently into the case wall. It is the part you cannot easily replace: extracting a damaged one means taking the movement out. The crown holds one or more gaskets and a small spring. Screwing it down draws the crown along the tube and squeezes those gaskets; unscrewing it lets the spring push the crown out to its winding position. Engagement is usually a turn and a half to three turns, no more, so a crown that keeps turning without either tightening or coming loose is telling you something is wrong inside.

Makers differentiate on the number of sealing surfaces rather than on the thread. Rolex's Twinlock crown seals in two zones and its Triplock, introduced in 1970, in three. More sealing surfaces means more friction, which is why a serious dive watch has a stiffer crown.

Where it came from

The screw-down crown reached the wristwatch with the Rolex Oyster case of 1926, built on a Swiss patent taken out the year before by Paul Perregaux and Georges Perret, which Rolex acquired. Before it, the stem opening defeated every attempt at a sealed wristwatch, and nearly a century later the design has barely changed.

Why it matters

The stem opening is the largest hole in a watch case and the one that moves, so it is the most likely route for water to get in. A pushed-in crown relies on a gasket held in place by a light spring load. A screw-down crown adds mechanical compression, and the seal improves rather than degrades as pressure rises.

The crucial point is conditional: the rating applies only when the crown is screwed fully home. Left unscrewed, even by a turn, the watch has no meaningful water resistance whatever the dial says, and a crown left out after setting is the single most common way a watch gets flooded.

How to use one

Unscrew counterclockwise until the crown springs free. Wind or set as usual. To close it, push the crown in and turn clockwise with light pressure until you feel the threads catch, then tighten only to gentle resistance. Never force it: cross-threading a case tube is a case repair, not a five-minute job, and over-tightening deforms the gasket.

Rinse a watch in fresh water and dry it before operating the crown after swimming in the sea or in a pool, so that salt and chlorine are not dragged into the tube.

Common misconceptions

A screw-down crown is not a permanent seal. Gaskets are rubber or synthetic, and they harden and compress with age, heat, soap and sun cream. A watch you swim in deserves a pressure test every year or two, and new gaskets at service.

Nor does a screw-down crown alone make a watch a diver. Case back, crystal, pushers and every gasket in the chain have to match, and a divers' watch has a whole standard of its own to meet.

No standard requires the mechanism. ISO 22810, which governs the words "water resistant" on an ordinary watch, and ISO 6425, which governs the DIVER'S marking, both specify results rather than construction: the case must hold pressure and the operating devices must resist a sideways force while immersed. Plenty of 100 meter watches seal on a pushed crown, and Panerai gets the same result with a lever bridge that clamps a push crown against its gasket, patented in Italy in 1955. Equally, a screw-down crown on a 30 meter case does not make it a swimming watch.

What to do when it goes wrong is a short list. A crown that will not catch is almost always grit or cross-threading, and our page on a crown that will not screw down works through it in order. Never use a tool for grip: alignment is the problem, not force. A replacement crown and stem with a pressure test afterward runs roughly $120 to $350 at an independent watchmaker, and a pressure test alone about $25 to $60, both indicative US figures before sales tax. If you swim with the watch, have it pressure tested every year or two. How a case seals as a system is in our guide to water resistance ratings.