The Rolex Datejust 31 reference 178240 represents the mid-size 31mm Datejust 31 in full Oystersteel — the elegantly proportioned middle ground between the larger 36mm men's Datejust and the smaller 26mm Lady-Datejust. Released in 2009 as the mid-size complement to the 116200 men's Datejust, the 178240 carried the proportions and styling of the modern Datejust scaled down for wearers who prefer a more refined watch presence on the wrist. The 31mm Oystersteel Oyster case is paired with the smooth polished Oystersteel bezel and the three-link Oyster bracelet with concealed Crownclasp — a refined choice that distinguishes the 178240 from the fluted-bezel Datejust 31 references with their busier visual profile. The pink dial features applied luminous hour markers, polished white gold hands, and the cyclops-magnified date window at 3 o'clock — the date complication that has defined the Datejust line since the model debuted in 1945. Powered by the Rolex Caliber 2235 self-winding chronometer movement — Rolex's smaller-diameter mechanical caliber developed specifically for the mid-size and ladies' Oyster Perpetual line — the 178240 beats at 28,800 vibrations per hour, carries COSC certification, and delivers a 48-hour power reserve. Sapphire crystal, screw-down Twinlock crown, 100 meters water resistance. Pre-owned.