• Case Diameter: 40 mm

• Case Thickness: Approx. 11.9 mm (slimmer than the previous generation)

• Lug-to-Lug: Approx. 47.5 mm

• Lug Width: 20 mm

• Material: Oystersteel and 18k yellow gold (Yellow Rolesor)

• Bezel: Fixed, polished 18k yellow gold with an engraved tachymetric scale

• Crystal: Scratch-resistant sapphire with anti-reflective coating

• Crown: Screw-down Triplock triple waterproofness system in 18k gold

• Pushers: Screw-down chronograph pushers

• Case Back: Solid, screw-down Oystersteel

• Water Resistance: 100 meters (330 feet) 

The Rolex 126503 is powered by the Caliber 4131, a fully in-house, self-winding mechanical chronograph movement introduced in 2023.  It is an evolution of the previous Caliber 4130, featuring significant technical and aesthetic upgrades while maintaining the same core dimensions. 

Core Technical Specifications

• Frequency: 28,800 vibrations per hour (4 Hz)

• Power Reserve: Approximately 72 hours

• Jewels: 44 (some sources cite 47 for specific components)

• Functions: Center hours, minutes, and seconds; small seconds at 6 o'clock; 30-minute counter at 3 o'clock; 12-hour counter at 9 o'clock. 

• Winding: Bidirectional self-winding via a Perpetual rotor.