Steel or stainless steel A2.

Steel electro zinc-plated.
Stainless steel bright.

R-clips are used for securing bolts and axles. They are easy to install and can be reused. The ends have no sharp edges.

Double coil R-clips have a flatter spring characteristics and are easier to install. The double coil allows a tether cable to be attached to prevent loss.

Form E: with single coil.
Form D: with double coil (coil direction can differ from the drawing).