When two different types of metals come in contact a chemical reaction occurs: Electrolysis uses moisture as catalysis at a molecular level to pass ions from one metal to the other. The process causes a deterioration of both metals similar to the effects of rust. Using the wrong type of fasteners causes a real concern due to the importance of the fastener itself. Electrolysis causes the fastener puncture to deteriorate and widen, allowing a water path and seepage. The photos show incompatible fastener types were used and electrolysis is occurring.