The Rolex Caliber 1166 is a manual-winding mechanical movement from the 1950s to early 1960s, part of Rolex’s compact 11xx series of hand-wound calibers. The 1166 is believed to be a GMT (dual-time) variant of the Caliber 1160, similar in purpose to the extremely rare Caliber 1165. Like its sibling, the 1166 added a 24-hour GMT hand to a time-only base movement, allowing the wearer to track a second time zone—an innovative function during a period when international travel and aviation were rapidly expanding.

Because of its rarity and the limited documentation surrounding it, the 1166 is regarded as a low-production or possibly prototype-level movement, used in very early Rolex or Tudor GMT-style watches.

Technical Specifications

• Type: Manual-winding

• Functions: Hours, minutes, 24-hour GMT hand

• Jewels: 17

• Frequency: 18,000 vibrations per hour (vph)

• Power Reserve: Approximately 42 hours

• Shock Protection: Incabloc or KIF (depending on version)

• Chronometer Certified: No

• Date Function: No

• Hacking Seconds: No

• Quickset Function: No

The 24-hour hand was likely non-independent, moving in sync with the standard hour hand, similar to early Rolex automatic GMT calibers such as the Cal. 1036.

Design and Features

Despite its simplicity and compact size, the Caliber 1166 maintained Rolex’s strong mechanical standards:

• Modified geartrain to support the 24-hour hand

• Three-bridge construction with rhodium-plated components

• Manual-wind only, no automatic rotor

• Shock-protected balance assembly

• Designed for smaller Oyster cases, typically in the 26–30 mm range

This movement would have been paired with either a rotating 24-hour bezel or a fixed bezel with dual-time markings to make the GMT function usable.

Watches Powered by Caliber 1166

The Caliber 1166 is extremely rare and was likely used in:

• Rolex or Tudor prototype GMT watches

• Very low-production travel watches made for specialized markets (e.g. pilots or military use)

• Possibly early Tudor Oyster Prince-style watches with GMT indicators

Any such watch would feature:

• Compact steel or gold Oyster cases

• 24-hour bezels or internal GMT scales

• Clean dials with minimal text—typically "Precision" or "Tudor" markings

• Manual-wind crown, no automatic rotor or date

Historical Context

The 1166 fits into the narrative of Rolex’s early exploration of GMT complications, alongside other rare manual calibers like:

• Caliber 1065 GMT / 1066 GMT – Early compact GMT experiments

• Caliber 1165 – Similar in design and function

• Caliber 1036 (automatic) – Used in the first Rolex GMT-Master Ref. 6542

Rolex ultimately focused its GMT production on automatic calibers, but these manual-wind variants show that GMT development was happening in multiple sizes and formats, possibly for different target markets or testing purposes.

Collectibility and Legacy

Due to its extreme rarity and limited documentation, the Caliber 1166 holds potential value for:

• Rolex historians and movement researchers

• Collectors of prototype or early GMT movements

• Vintage watch specialists focused on rare dual-time complications

• Museum collections, particularly if a confirmed example exists in original condition

A verified Caliber 1166 watch, in a correct case with matching dial and bezel, would be considered exceptionally rare and highly desirable.

Final Thoughts

The Rolex Caliber 1166 is a mysterious yet fascinating chapter in Rolex’s horological history. A compact manual-wind GMT movement, it reflects the brand’s early innovation in travel watch complications during the formative years of the Jet Age. Though few (if any) examples are seen today, its existence suggests Rolex was experimenting broadly with GMT mechanics long before the function became standard in their automatic GMT-Master line. For collectors and enthusiasts of obscure vintage Rolex movements, the 1166 is a true hidden gem.