Rolex Submariner 116613LB is the reference in this note. Lay the watch on a plain cloth under a lamp. Read the case flank before you read the dial, because the flank shows tool marks and a polished edge that a photo crops away. Count the lugs. Note whether they are drilled. A drilled lug means the strap can be changed with a spring bar, and the hole should be round rather than oval from a bar that was forced. Flex the bracelet at the first link. Stretch that does not return is wear, not a style. The clasp should close with one click and sit flat. If it stands proud, the fold has been bent. Look through the crystal at an angle. Dust on the inside of the glass is a different problem from a scratch on the outside. Write which one you see. Then set the hands and watch them for a full minute so you can say whether the seconds hand ticks or sweeps. That single observation tells you the kind of movement in the case. Record it next to the reference engraving. The two notes belong together.
How it differs
Rolex Submariner 116613LB is a diver-shaped case. On the wrist, check that the bezel insert sits flat, that the pip lines up with 12, and that the bracelet or strap meets the lugs without a rock. People change the insert, the clasp, and the crystal on this shape more often than they change the case itself. A unidirectional bezel should click. A bezel that freewheels needs a note, not a guess about the rest of the watch.
What to check on a used piece
What to check on a used Rolex Submariner 116613LB starts with the engraving. The reference to read is 116613LB. Then check end-link play, clasp fold, and whether the hands pass each other. There is no price in this note.
Common mods
Common changes on a used diver are a new bezel insert, a shortened bracelet, a different clasp, and a crystal with a fresh lip. Describe each one. Do not treat a new insert as a different reference if the case engraving is unchanged.
What people change
On the Rolex Submariner 116613LB, people change the bracelet, the case, or the movement.