A ring key is a ring ended spanner, not an open jaw, normally 12 points like a socket. A ring key is more desirable than an open ender as it will engage the nut in 12 positions as opposed to 6 with an open ender, as a nut has 6 flats on it. Stahlwille Motor are a West Germany brand who start their spanners with the best tool steel available and go from there, as West Germany are no longer a country, the company are discontinued. Modern spanners start with the cheapest steel from China and go from there. Vanadium steel alloy is hard, Molybdenum steel alloy is more forgiving and less prone to fracture; Stahlwille Motor perfected a balance between hardness and flexibility, engineers call it 'toughness'.