I felt like there weren't many key cases on the market that could be used even if you only had one hand free, so I made one. It uses Roroma leather, sold by Nakamura Chinosuke Shoten Co., Ltd. in Japan. This is a heavy-duty leather made from domestic steerhide (adult cow) that has been tanned twice with vegetable tannins and thoroughly infused with oil and wax. Because the leather is thick, it takes 1.5 times longer than normal tanning to finish. As a result, it develops a gem-like luster when polished, and you can enjoy the aging process. The 4th and 5th images show keys actually attached. When you open the spring hook and shake the main body, the keys will come out. If you attach a key reel or similar to one of the rings, you can easily take out, operate, and store the keys with one hand. It can hold 1-2 keys. Since it's a minus screw, you can attach the keys by using pliers to hold the hardware on the opposite side of the screwdriver and turning it counterclockwise, using a cloth or something to prevent scratches. I actually use the same model that I'm selling, and it's super convenient.