Why should I use a retaining ring instead of a screw, nut and threads, cotter pin and washer and other traditional fasteners?
Retaining rings can do the same job for a lot less. A simple groove is all thats needed to accommodate a retaining ring. Other fastener methods, like nuts, require machining threads, which is a lot more costly. They also require at least two components to function (Ex. Cotter pin and washer, nut and washer), which adds to the costs.
