U2 (EZM5) Dive Watch
Sinn U2 S
The case of this dive watch is manufactured from submarine steel. Conventionally stainless steel for the watch case has no real resistance to sea water. Strictly seen such cases are not suitable for permanent use in sea water. In search of a steel, which meets the higher quality requirements, the Sinn engineers eventually made a find at the German submarine shipyard Howaldtswerke-Deutsche Werft and the Nordseewerke Emden/GmbH steel from the current German submarine production is exclusively delivered.
This material is not only extremely resistant to sea water, but has also the highest anti-magnetic quality. A residual magnetism still occuring in the conventional and high-quality stainless steel watch cases of grade 316 L, is not possible in the case of submarine steel.
Another major advantage of this steel for watchmakers lies in its special property to be tegimented. The submarine steel can be hardened to 1500 Vickers. Thus, the previous hardness of the Sinn tegiment case is exceeded by about 300 Vickers. For comparison, the base hardness of conventional stainless steel (316 L) is approximately 220 Vickers.
Another special feature of this watch is the captive and hardened diving bezel. To avoid removal of the rotating ring by hard knocks, it is not connected with the middle part of the case by a snap mechanism as usual, but a newly developed mounting device holds it securely in place. The detent is ball-mounted three times; slightly radially offset locking ball positions conserve the ring gear, ensure the function and provide a solid and secure engagement.