There are four types of waterproof structures for waterproof water meters:
1. Threaded tightening waterproof structure. This is the most common and primary type of waterproof meter, and all domestic meters adopt this structure. Its characteristic is that the back cover and the meter case are connected by threads, and a sealing washer is pressed. The edge of the back cover has 8, 10, or 14 symmetrical angle edges, which can be opened with a meter opener. Watches from Soviet brands like Pilot and Russian brands, although they have no threads on the bottom but use a threaded rear ring to seal, should also belong to this category.
2. Compression-type waterproof structure. The bottom shell is a concave steel bowl, and the meter mechanism is installed inside the steel bowl. After pressing the tight ring and the watch crystal, the main shell frame tightly fastens the meter case, providing relatively good waterproof performance. Its characteristic is that there is no thread on the meter case, and the back cover is a rolled round edge shape. The edge of the cover has a sealing washer, which relies on tight compression to fit together, and can be pried open with a blade. However, the winding stem (commonly known as the self-winding rod) is a double-section rod, and water can easily accumulate at the joint and cause rusting. Many imported Roman watches fall into this category.
3. Knife-lift back cover waterproof structure. This type of waterproof meter is often overlooked and mistakenly regarded as an ordinary meter. Although it uses a knife to lift the back cover like an ordinary meter, it is much tighter. The watch crown and back cover are both padded with rubber rings, which can still serve a waterproof function. The renowned Omega watch once adopted this type of waterproof structure.
4. Bite-edge waterproof structure. It differs from the threaded bite-edge type in that there are no threads. The main shell frame and the bottom shell have interlocking concave and convex grooves. This structure is only seen in Enicar brand watches.