The short answer

A fake Rolex Explorer II ref. 16570 gives itself away in four places: the GMT hand and how it sets, the dial printing, the engraved 24-hour bezel, and the case size. The real reference is a 40mm stainless steel watch made from 1989 to 2011 with a caliber 3185 or 3186 inside. If the watch in front of you measures 42mm, beats at 21,600 vibrations per hour, or has a 24-hour hand that will not move on its own, it is not a 16570 no matter what the caseback says.

What the 16570 actually is

The 16570 replaced the 16550 in 1989 and stayed in the catalog until 2011, when the larger 216570 took over. Case size is 40mm with 20mm lugs and a Twinlock screw-down crown. The crystal is sapphire. The bezel is fixed steel with engraved 24-hour numerals, and there is no rotating action, so any bezel that turns is wrong. Water resistance is rated at 100 meters. Dials came in matte black or white, with the white "Polar" version now the more sought-after of the two. Hands are hour, minute, small seconds, and a 24-hour hand with an arrow tip.

Case and dimensions

Measure it. A 16570 is 40mm across the bezel without the crown, not 42mm, not 39mm. Lug to lug is roughly 47mm. Genuine examples are comfortable on a 7-inch wrist in a way the wider 216570 is not. Earlier production has drilled lug holes; later pieces do not. Look between the lugs at the 12 side for the reference stamp and at the 6 side for the serial, both stamped into the metal rather than laser-etched on top of it. Inside the caseback you should find the reference and case numbers along with the Rolex mark. Later production added rehaut engraving around the dial, and the lettering there is thin and even, not blurry or heavy.

The GMT hand test

This is the fastest way to sort a real one from a fake. Unscrew the crown, pull it to the first click, and the date quicksets. Pull to the second click and the seconds stop, which means the movement hacks. Now turn the crown slowly. On a genuine caliber 3185 or 3186, the hour hand jumps in one-hour increments while the minute hand stays put, and the 24-hour hand travels along with the hour hand. Many fakes built on a modified ETA or clone GMT movement do the opposite: the 24-hour hand jumps and the hour hand stays still, or the 24-hour hand runs on its own gear and drifts out of alignment with the bezel. Set the watch to a known time and check that the 24-hour hand points to the correct hour on the bezel after a full rotation.

Dial printing and lume

The word ROLEX under the coronet is crisp, evenly spaced, and the feet of the letters do not touch. Tritium dials carry "T SWISS MADE T" or "SWISS - T < 25" at the bottom, and tritium from that era has usually aged to a warm cream that matches the hands. Later dials read "SWISS MADE" with Luminova or Super-LumiNova, which stays pale green. Fakes often use painted yellow lume to fake patina, and the mismatch between the hand lume and the dial lume is a tell. The date sits in a window with around 2.5x magnification under the cyclops, and the date font on a genuine watch has a flat-topped 4 and a clean serif on the 1.

Bezel engraving and crystal

Bezel numerals on a real 16570 are cut deep and filled cleanly, with sharp edges and consistent depth from the 24 at the top around to the 12. On fakes the numerals are shallow, wide, or filled with paint that sits proud of the surface. The sapphire crystal has a laser-etched coronet at the 6 o'clock position, visible under a loupe at an angle. It is tiny, maybe a millimeter across, and sits right at the edge of the crystal. A fake either lacks it or has one that is too large and too dark. Sapphire also has a distinct hardness and temperature feel, and cheap glass shows scratches that sapphire will not.

Bracelet and clasp

The correct bracelet for the 16570 is an Oyster with solid end links, reference 78790 or 78790A, with an Oysterlock clasp. Links are thick and the center links on polished examples have a mirror finish that flows into the case without a visible seam. End links sit flush against the lugs with no gaps. The clasp carries stamped codes for the bracelet reference and a date code, and the coronet on the clasp is stamped, not cast with soft edges. Fold the bracelet over your finger and listen. A genuine Oyster is quiet. A fake rattles.

Movement and feel

The caliber 3185 runs at 28,800 vibrations per hour, 31 jewels, around 50 hours of power reserve. The 3186 arrived in later production and is a revised version of the same architecture. Winding feels smooth and slightly damped, with a fine click. A watch that winds with a gritty, dry grind or that has a stiff, buzzy rotor is suspect. Ask for a timing reading on a machine. A genuine movement will hold a steady rate with low beat error, while many fakes show large positional variation.

Why the numbers on a fake never add up

Counterfeiters copy the look, not the logic. They build a 40mm case around a movement that was never designed for a jumping hour hand, so the GMT function gets faked at the cost of correct behavior. They use dial printing that looks fine in photos but falls apart under a loupe. They engrave the bezel with a CNC machine that leaves rounded edges. Every one of those compromises is visible if you know the reference.

Box, papers, and price

Genuine 16570 examples with a full set (box, booklets, hang tags, punched warranty card) carry a premium, and the Polar dial even more. Prices on the secondary market sit well into four figures and climb for clean, unpolished cases. If someone offers a complete set for a fraction of what dealers ask, the watch is not real. A sealed caseback with no service history and a seller who refuses a movement photo are the same warning sign.

One legal note

Buying or selling a counterfeit Rolex is trademark infringement in the US, and watches shipped through customs can be seized and destroyed. If your interest in the 16570 is authentication, take the watch to a Rolex-trained watchmaker or a service center and get the movement inspected. Serial numbers and dial details can be copied. The calendar mechanism inside cannot.