Rinko is the Japanese system of packing bikes for train travel. It’s an elegant way of converting your bike into a small package that you sling over your shoulder and carry on trains, subways, buses or in other crowded places. It is very satisfying to ride up to a train station, and 15 minutes later, having reduced your bike to a neat, small package. One advantage of Rinko is that the bike doesn’t need couplers or other parts that add cost and complexity, and compromise the ride quality. Consider a few small details when designing the frame, use a few special parts, and a standard bike can be made to Rinko.
There are many different Rinko systems, and this nut is intended for the Alps-style system, which removes the fork and part of the rear fender to reduce the bike to the smallest possible package.