Metric tight caps, thanks to their special design, do not require an additional washer or o-ring, avoiding the risk of losing, misplacing or omitting the washer during installation. Shaped with outside vertical ribs to ease fitting and removal with a tool. They are recommended for multiple applications such as hydraulic units: gear pumps, vane pumps, control valves, cylinders, commercial vehicle steering systems. In most cases the liquid is inside the application and they are tested under high pressure, which the threaded cap must resist.