The question arrives in every listing and half the forum threads ever written: what is actually the difference between a GMT-Master and a GMT-Master II? The answer is one mechanism. On the original GMT-Master, the extra 24-hour hand is geared to the ordinary hour hand; they turn together, always agreeing, and the only way to read a second time zone is to rotate the bezel. On a GMT-Master II, the ordinary hour hand can be set by itself, jumping in one-hour steps without stopping the watch or disturbing the minutes, while the 24-hour hand stays put on home time. Land in a new country, click the local hand forward a few hours, and the bezel is freed up for a third zone. That is the whole difference. Everything else, the shared case language, the shared bezels, the shared name on the dial minus one Roman numeral, has confused buyers for forty years, which is what this dossier is for.
One movement family, one chained hand
The original line runs from the 6542 of the mid-1950s, built to Pan Am's specification so its crews could hold home and destination time at once, through the 1675, the reference that carried the design for twenty-one years, to the 16750, which added the quickset date and doubled the water resistance at the start of the 1980s. Across all three, the 24-hour hand is chained to the hour hand. The watch is honest about it: it displays one time in two formats, and the bezel does the traveling. For nearly three decades that was what GMT-Master meant, and the airlines were satisfied.
1983: the fork
The 16760 changed the definition. Its new caliber 3085 decoupled the hands, giving the local hour its independent one-hour jumps, and the movement's extra height thickened the case enough that collectors named the watch the Fat Lady. Rolex named it something more consequential: GMT-Master II. It brought a run of firsts beyond the mechanism, the family's first sapphire crystal, first white gold marker surrounds, and the debut of the red-and-black Coke bezel, its only bezel. What it did not do was replace the GMT-Master. The 16750 stayed in the catalog beside it, and the fork was open.
The decade of both
In 1988 Rolex renewed both lines at once and made the fork explicit. The 16700 carried the GMT-Master name with caliber 3175, chained hands and all; the 16710 carried the GMT-Master II name with caliber 3185 and the independent hour. On the wrist they are nearly identical, which was the point. The choice was the mechanism, and here is the detail that kills the budget myth: the price gap was trivial. A 1991 UK retail list has the GMT-Master at 1,451 pounds and the GMT-Master II at 1,484, a difference of 33 pounds on a fourteen-hundred pound watch. Rolex was not selling a cheap one and an expensive one. It was selling two answers to the same question at the same money, and for eleven years customers kept choosing both.
The old line even kept an advantage. The 16700's date is quickset through the crown, while the 16710 sets its date by cycling the jumping hour hand, a small daily convenience traded for the traveling one. The 16700 came only in Pepsi or black; the 16710 offered Pepsi, black, and Coke, which turned out to be that bezel's final appearance in the family. In 1999 Rolex quietly ended the 16700, and with it the GMT-Master name after forty-five years. The fork closed not because the original lost, but because the II had finished absorbing everything the original did.
After the fork
Every Rolex GMT since 1999 is a II. The 116710LN brought the ceramic bezel era in 2007, and the 116710BLNR answered the two-color ceramic problem in 2013 with the blue-black bezel Rolex had implied could not be fired in one piece. The full succession, both tines of the fork, is laid out reference by reference in the family file, where the lineage strips on the Master pages end at the 16700 in 1999 and the II pages carry on, because that is what actually happened.
Which one is on the table
For a buyer weighing a 16700 against a 16710, the file's guidance is short. Read the dial: GMT-MASTER and GMT-MASTER II are printed plainly, and a seller's title is not the dial. Confirm the behavior: pull the crown and set the hour; independent one-hour jumps mean a II, and a date that quicksets from the crown means a 16700. Check the era with the serial lookup, and then hold both answers honestly: the 16710 is the more capable watch and the more versatile one, three bezels against two, eighteen years of production against ten. The 16700 is the last of the original faith, the shorter run, and the rarer sight, the final watch to wear the name that started the whole family in 1954. Neither answer is wrong. The fork existed because both were right, and eleven years of side-by-side sales is the proof in the record.