The replica royal oak 15407ST is the steel double balance wheel skeleton — the same openworked Cal. 3132 that AP puts in precious-metal cases, housed here in stainless steel. You see every bridge, wheel and spring through the dial. Two balance wheels connected by a shared differential improve timekeeping stability by averaging out positional errors. At 41mm and roughly 10.4mm thick, it wears like a standard Royal Oak from the outside. The view from the front is where it separates entirely.
Double Balance Wheel Movement
The Cal. 3132 runs two balance wheels operating on a single shared escapement. Each wheel oscillates independently, and a differential mechanism averages their rates. The purpose is redundancy and stability — if one balance is affected by a positional shift, the other compensates. The practical gain is tighter timekeeping across all six positions compared to a single-balance caliber.
Both balance wheels are visible through the openworked dial, beating in tandem near the centre of the movement. The rest of the architecture — mainspring barrel, gear train, winding rotor — is exposed through cut-away bridges finished with bevelled edges and striping. There is no date complication. AP removed it to keep the dial symmetrical, which is the right decision on an openworked layout. See the rose gold 15407OR for the same movement in a warmer case material.
Steel Skeleton Proportions
Most skeleton watches in the Royal Oak family come in precious metals. The 15407ST puts the same movement into stainless steel, which changes the economics and the wearing experience. Steel is harder than gold — it holds its polish longer and resists desk-diving scratches better. The trade-off is visual: steel bridges and a steel case read cooler and more industrial than the warm tones of a replica royal oak 15407ST in rose gold.
At 10.4mm thick, this sits right between the 8.1mm time-only references and the 12.4mm chronographs. The integrated bracelet tapers from 24mm at the lugs to about 18mm at the clasp, keeping the profile close to the wrist. It wears lighter than it looks because the openworked movement removes material that a solid dial would add. Browse the full Royal Oak collection or check our FAQ for common questions about skeleton references.
| Reference | 15407ST.OO.1220ST.01 |
| Case | 41mm · stainless steel |
| Bezel | Octagonal · 8 hexagonal screws |
| Dial | Openworked · double balance wheel visible |
| Crystal | Sapphire · AR coating |
| Caliber | 3132 · automatic · double balance wheel · 45h reserve |
| Bracelet | Stainless steel · integrated |
| Buckle | Stainless steel · AP folding clasp |
| Water | 50m / 5 ATM |
| Functions | Hours, minutes |
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