The Datejust 31 is the mid-size member of the Datejust line, a self-winding, date-displaying watch built on the Oyster case. Reference 278240 is the all-Oystersteel version of the current Datejust 31 generation, fitted with a smooth domed bezel rather than a fluted or gem-set one.
This generation of the Datejust 31 was introduced under the Datejust collection at Baselworld 2018, when the model moved to the caliber 2236 movement with a silicon hairspring. The full-steel 278240 with the smooth domed bezel is documented as reaching the market in 2019, replacing the earlier reference 178240.
It sits as the entry point into the Datejust 31 range, below the White, Yellow, and Everose Rolesor and solid-gold configurations. It is a regular-production model, not a limited edition.
The configuration described here is the silver dial with applied baton markers on an Oyster bracelet, catalogue variant m278240-0005.
The dial is silver with a sunray finish, produced by brushing fine grooves outward from the centre so the surface shifts in tone as the wrist moves. The colour is applied over the finish and sealed with a light coat of varnish.
Hour markers are applied baton indices filled with luminous material, with a coronet at 12 o’clock. The hands are baton-style and luminous. The luminous display is Rolex Chromalight, which emits a blue glow in low light.
The date sits at 3 o’clock under the Cyclops lens on the crystal. Printed dial text reads ROLEX with the coronet at the top, OYSTER PERPETUAL and DATEJUST below the centre, SUPERLATIVE CHRONOMETER OFFICIALLY CERTIFIED above 6 o’clock, and SWISS MADE at the base of the dial.
The case is the round Oyster case in 31 mm, built on a monobloc middle case with a screw-down case back and a screw-down winding crown. The crown uses the Twinlock double waterproofness system. Water resistance is 100 metres.
The crystal is scratch-resistant sapphire with the Cyclops lens magnifying the date. Measured examples put case thickness at approximately 11 mm and lug-to-lug at approximately 37 mm; Rolex does not publish these two figures for the reference.
The bezel is a smooth domed bezel in Oystersteel. It is fixed and decorative, with no timing or measurement scale.
This reference is fitted with the Oyster bracelet, a three-piece solid-link bracelet in Oystersteel. The Oyster is the flat, three-link design, distinct from the five-link Jubilee offered on other suffixes of the same reference.
The clasp is a folding Oysterclasp. It carries the Easylink comfort extension, which lets the wearer lengthen the bracelet by approximately 5 mm without tools.
The 278240 was also sold on a five-link Jubilee bracelet with a concealed folding Crownclasp under separate catalogue variants. The bracelet described on this page is the Oyster.
The movement is the Rolex caliber 2236, a self-winding mechanical movement made in-house. It runs at 28,800 vibrations per hour (4 Hz), carries 31 jewels, and holds a power reserve of approximately 55 hours.
Winding is bidirectional through a Perpetual rotor. The oscillator uses the Syloxi hairspring in silicon with a patented geometry, paired with Paraflex shock absorbers. The movement is a Superlative Chronometer, certified by COSC and then tested again by Rolex after casing to a rate of -2/+2 seconds per day.
Functions are centre hour, minute, and seconds hands, plus an instantaneous date with rapid setting. A stop-seconds function halts the seconds hand when the crown is pulled out, for setting the time to the second. The date is advanced through the crown in its intermediate position.
The case, bezel, and bracelet are Oystersteel, the corrosion-resistant steel from the 904L family that Rolex uses across its steel watches. It takes and holds a high polish and resists marking in daily wear.
The crystal is synthetic sapphire, chosen for scratch resistance, with the integrated Cyclops date magnifier. The applied dial markers and hands carry Chromalight luminous material for low-light legibility. The clasp is Oystersteel, matching the bracelet.
The overall material character is a single-metal steel watch built for everyday durability, with sapphire and luminous furniture as the functional additions.
A full set for a 2026 example of this reference includes:
Older version
Newer version
The changeover from the cream/beige outer box to the green outer box happened around early 2025, so a 2026 example is expected to carry the Gen 2 packaging. Rollout varied between retailers, so some watches sold in 2025 could legitimately receive the earlier Gen 1 box. A generic or mismatched box lowers the completeness of a full-set listing.
A 2026 example is covered by the Rolex five-year international guarantee, which applies to all new Rolex watches and runs from the date of purchase recorded by the Official Rolex Jeweler. The guarantee is documented on a plastic international guarantee card, the simplified dark-green format used from approximately mid-2020. Coverage is worldwide and transferable with the card.
Older version
Newer version
A 2026 example carries the Gen 2 card, and its five-year guarantee is active well beyond today’s date. The card is the primary authentication document and is completed and dated at point of sale, so a correctly recorded card is central to a full-set valuation; a blank, photocopied, or mismatched card is a concern. A watch returned through service may carry post-service documentation rather than, or alongside, the original card.
At 31 mm the Datejust 31 wears as a true mid-size watch, between the 28 mm Lady-Datejust and the 36 mm Datejust. Measured thickness of around 11 mm keeps it low on the wrist and easy under a cuff.
The Oyster bracelet tapers from the case toward the clasp, and the Easylink extension allows a quick 5 mm of on-the-fly adjustment for changes in wrist size through the day. The 31 mm case and mid-size proportions suit smaller to medium wrists, roughly in the 5.5 to 6.75 inch range.
It reads as a versatile everyday and dress watch rather than a tool watch, appropriate for both formal and casual wear.
Reference 278240 is defined by two constants across every example: an Oystersteel 31 mm Oyster case with a smooth domed bezel, and the caliber 2236 movement. Within those constants it was produced in a wide range of dials and in two bracelet choices.
Dials
Bracelets
Closely related references in the Datejust 31 family that are separate watches with different specifications include:
Specifications do not carry across from those references to 278240.
Personalized, end-to-end service to help you buy, sell, and trade with ease
