Ulysse Nardin

MTR
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Excellent contribution, LwC — and I fully agree

The myth that water resistance requires a screw-down crown deserves more nuance.

You’re absolutely right — the primary barrier to water ingress is the quality and condition of the gaskets (o-rings) around the crown stem and tube. The screw-down mechanism is often more about mechanical redundancy than baseline water resistance. In fact, many ISO 6425-certified divers — especially vintage models — never had screw-down crowns and still performed reliably, provided the seals were intact and regularly serviced.

What I have learned when talking to various watchmakers: the screw-down crown does serve two important secondary functions:
1. Mechanical retention: It helps prevent accidental crown extension or displacement, which can be a real issue during dynamic activities (diving, impacts, gloves).
2. Consistent seal compression: When screwed down properly, it ensures even and repeatable gasket pressure — especially valuable as seals age or under thermal cycling.

What’s often overlooked is that a well-executed non-screw-down crown can actually be less prone to user error. Cross-threading, overtightening, and misaligned threads are all real risks with screw-down crowns — and they can compromise the case far more than an o-ring ever would. I never thought about that before a very experienced watchmaker explained this to me.

A brilliant alternative is the lever-based crown protection system used by Panerai. Rather than relying on threads, the crown is pressed against its gaskets by a locking lever, which:
• avoids thread wear entirely,
• adds robust lateral protection,
• and gives the wearer clear, unambiguous feedback that the crown is secured.

It’s a smart engineering solution that achieves strong water resistance without the usual mechanical risks of a screw-down system.

I never had my moment of “confidently unscrewed aquatic exploration.” My nerves wouldn’t allow this. 😅