Seamaster Aqua Terra 150M Master Co-Axial 38.5 Yellow Gold / Diamond / MOP

In Context

At 38.5 mm it sits just under the modern norm — the band that suits the widest spread of wrists. The case back is open, so the movement is visible without taking the watch apart, and the sapphire crystal will resist everything short of deliberate abuse. 150 m is genuine swimming resistance — more than the shape of this watch suggests it would need.

The movement winds itself from the motion of your wrist. 60 hours of reserve is enough to set it down on Friday evening and find it still running on Monday. At 25,200 vph the seconds hand advances 7 times a second.

231.58.39.21.55.002 stands on its own in this catalogue — no other reference here shares its base number. It pairs a white dial with a yellow gold case.

The 8501 is the 8500 with an 18-carat gold rotor and balance bridge, fitted only to gold-cased watches. It powers 59 watches in this library. The [8500](/calibers/omega-8500) is Omega's first in-house co-axial caliber, with two barrels in series for a 60-hour reserve, a free-sprung balance, 39 jewels and a 29 mm diameter at 25,200 vph. The 8501 is mechanically identical; the rotor and balance bridge are made in the gold of the case so that the view through the display back is consistent. Omega applies the same convention to the [8521](/calibers/omega-8521), [8701](/calibers/omega-8701) and [8807](/calibers/omega-8807). In the library it sits under 24 [Aqua Terras](/brands/omega/aqua-terra), 19 [Constellations](/brands/omega/constellation), 10 [De Villes](/brands/omega/de-ville) including the red gold Hour Vision, and 6 [Planet Oceans](/brands/omega/seamaster-planet-ocean). Cases run from 38 mm to 45.5 mm, with 38 mm and 38.5 mm the most common at 19 and 18 references. The [8900](/calibers/omega-8900) is the Master Chronometer successor to the whole 8500 family.

58 other watches in the library run the Omega 8501.

Omega

Constellation Co-Axial 38 Red Gold / Brown

12350382113001 · 38 mm

Omega

Seamaster Aqua Terra 150m Master Co-Axial 41.5 Yellow Gold / Champagne

231.53.42.21.08.001 · 41.5 mm

Omega

Constellation Co-Axial 38 White Gold / Diamond / Black

12355382151001 · 38 mm

Omega

Constellation Co-Axial 38 Yellow Gold / Champagne

12350382158001 · 38 mm