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Assorted Accessories, General Accessories
Having a spare as a technical diver is routine. This Over Pressure Relief Valve can get you out of a jam if you find a problem with the one attached to your BCD. Many technical divers custom build their own BCD. OMS supplies all the required parts to do just that.
Just check that the size of the thread is the one you need. I have a Dacor BC and the thread was not the same, so I had to make a mix of the old and new valves.