Connector contact resistance may become unstable if fretting occurs. Such motions result in the formation of insulating oxides on the surface of base metal contacts or organic polymers on contacts made of platinum group metals. These degradations are termed fretting corrosion and frictional polymerization, respectively. Motion may be caused by external vibration or fluctuating temperature. The lower the frequency of movement, the fewer the number of cycles to contact failure. Increasing the contact normal load or reducing the amplitude of movement may stabilize the connection. Tin and palladium and many of their alloys are especially prone to fretting failure. Tin mated to gold is worse than all-tin contacts. Gold and high gold-silver alloys that are softer when mated to palladium stabilize contact resistance since these metals transfer to the palladium during fretting; but flash gold coatings on palladium and palladium nickel offer marginal improvement for the gold often quickly wears out. Dissimilar metal contact pairs show behaviors like that of the metal which predominates on the surface by transfer. Contact lubricants can often prevent fretting failures and may even restore unlubricated failed contacts to satisfactory service.