Sea-Dweller (4000)

Outright replicas of the Sea-Dweller 16600.

• Lug hole architecture: fakes based on Submariner tooling sometimes retain the lug holes visible from the front -- the 16600 has no lug holes
• Helium escape valve that is the wrong shape (circular rather than oval) or sits at the wrong position relative to 9 o'clock
• OSVERK clasp mechanism that lacks the two-step fold-over ratchet -- a simpler folding clasp is the most common hardware shortcut
• Case finishing with polished lug tops rather than the correct brushed finish on the lug faces and polished lug flanks

Bracelet and clasp substitutions on genuine-case examples.

• Non-OSVERK clasp on an otherwise genuine case and dial
• Later Glidelock clasp hardware (from post-2007 production) on an early 16600 serial
• Bracelet end links from the Submariner 16610 fitted to the Sea-Dweller case (different seating geometry)

Original: Oval-shaped helium escape valve at 9 o'clock position. The valve body has a specific diameter and thread engagement depth for this reference. Rolex machined the 16600 valve to precise tolerances for saturation diving operations.

• Valve diameter inconsistent with known 16600 production -- aftermarket valves are sometimes slightly oversized or undersized
• Valve that turns freely without any resistance (the genuine valve has a controlled torque feel from the sealing mechanism)
• Thread engagement that shows gaps or uneven seating against the case midband
• Tool marks around the valve perimeter indicating non-Rolex removal and replacement

Original: Twinlock winding crown with two dots on the crown side (visible under magnification). The Twinlock system provides two sealing points for water resistance, appropriate to the 4000ft/1220m rating.

• Crown with three dots (Triplock) -- the Triplock crown belongs to the Deepsea 116660 and later, not the 16600
• Crown with no dots (Quickset crown from other Oyster references) indicating a non-matching replacement
• Crown stem that sits proud of the case band at rest -- the 16600 crown seats flush when pushed to the winding position

Original: Oyster bracelet with the OSVERK glide-lock clasp: a two-step fold-over mechanism with a specific ratchet engagement. The clasp bears a date code on the inner arm indicating manufacture year.

• Simple folding clasp without the OSVERK two-step ratchet mechanism -- a common bracelet substitution on the secondary market
• Glidelock clasp from the post-2007 generation (different micro-adjustment mechanism, not correct for 16600)
• Bracelet end links with visible gaps against the case horns -- period-correct end links seat flush
• Date code on the clasp arm that falls outside the 1988 to 2008 production window

Original: "SEA-DWELLER" text (capitalization and spacing confirm this is not the earlier Double Red 1665). The 16600 has single white text only; the Double Red 1665 with two lines of red text is an entirely different, earlier reference.

• Any red text on the dial -- the 16600 does not use red dial text; red text is the Double Red 1665 (ref. 1665) or the modern 126600
• Dial text claiming the "DOUBLE RED" designation -- wholly wrong for the 16600
• Depth rating inconsistent with the 4000ft/1220m specification printed on the 16600

• Solid caseback -- no exhibition window
• "ROLEX OYSTER PERPETUAL DATE SEA-DWELLER" text on the outer ring
• "SUPERLATIVE CHRONOMETER OFFICIALLY CERTIFIED" on a middle ring
• Serial engraved between the lugs at 6 o'clock
• Reference 16600 engraved between the lugs at 12 o'clock
• Solid lug architecture: no lug holes visible from the front or side -- the lugs are a single machined piece, distinguishing the Sea-Dweller from the Submariner (which has lug holes)