They fit into grooves in the side of the shaft for a snug fit.
External-E Retaining Ring, Steel 1/2 in Shaft Dia, 12 PK Great for projects such as engines and locking mechanisms. as they are used to secure parts onto a shaft. X1 E-Clip / Circlip / E-ring - Side-Mount External Retaining Rings are fasteners that fit into the radial grooves of shafts - holes and are spring-loaded to ensure that they stay securely in place..