Snake rods have a “taper lock” system to secure them from coming apart in the pipeline.
To assemble the rods screw the thinner end into the larger end until the rod jams in place.
Once jammed in place the rods will resist coming apart again and the hook spanner will be needed to unscrew the rods. To unscrew the rods place the hook on the end of the outer spring and rotate to break the “taper lock”.