Whenever the rear brake drum or wheel hub is removed, it is necessary to replace the cotter pin. This secures the nut so that it can never loosen beyond the location of the cotter pin.
Loosening of the nut is almost always due to the fact that it was not tightened to the proper torque. Consult your shop manual for the correct torque and never tighten the nut haphazardly.
The dimensions are provided as a supplement in case you wish to use the cotter pin for other purposes.
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