What is Norwegian coupling?

A Norwegian coupling or claw hammer coupling or pickaxe coupling is a manual coupling consisting of a central buffer with a mechanical hook that drops into a slot in the central buffer. The system is only found on narrow gauge railways of 1,067 mm or less, such as Western Australian Government Railways, the Ffestiniog Railway and the Welsh Highland Railway, where low speeds and reduced train loads allow a simpler system. Norwegian couplings are not particularly strong, and may be supplemented by auxiliary chains. Not all Norwegian couplings are compatible with one another as they vary in height and width, and may or may not be limited to one hook at a time.