Damage Condition

Pits like spot corrosion on balls and raceways.

Possible Causes Caused by an electric current, creating sparks through a thin oil film, between the contact points of the raceways and balls while a linear guide was in operation (Electric potential difference between a rail and a ball slide) Countermeasures Provide an electric circuit so that the current does not pass through the linear guides
Electrolytic Corrosion

Part: Electrolytic corrosions on a raceway of rail
Symptom: Worn black pits
Cause: Sparks due to an electric current between rail and a ball slide

Source: NSK