The waterproof structures of Omega water meters come in four varieties:
1. Threaded tightening waterproof structure. This is the most common and primary type for waterproof watches, and all domestically produced watches adopt this structure. Its characteristic is that the back cover and the watch case are connected by threads, with a sealed washer pressed in between. The edge of the back cover has 8, 10, or 14 symmetrical angle edges, which can be opened with a watch opener. Watches from Soviet brands like Pilot and Russian brands, although they lack threads on the bottom, use a threaded rear ring for closure, should also be classified under this category.
2. Compression-type waterproof structure. The bottom case is a concave steel bowl, with the watch mechanism installed inside. A tight ring and watch crystal are pressed on top, and the main shell frame tightly secures the watch case, providing relatively good waterproof performance. Its feature is that the watch case lacks threads, and the back cover is round-edged. The edge of the cover has a sealing washer, relying on tight compression for its seal, which can be pried open with a blade. However, the winding stem (commonly known as the self-winding rod) is a double-section rod, making it prone to storing water and rusting at the connection point. Many imported Roman watches fall into this category.