Electroless plating puts a coating of nickel on the substrate without any electric current needed. The substrate "cathode" in this case (there is no anode) acts as a catalyst to start a chemical reaction that causes nickel ions in the electrolyte solution to be reduced and deposited on the substrate. The nickel coating also acts as a catalyst and keeps the reaction going until the part is removed from the bath. Thus, relatively thick coatings can be developed. Coatings are typically between 0.001 in and 0.002 in thick. Unlike electroplating, the electroless nickel plate is completely uniform and will enter holes and crevices. The plating is dense and fairly hard at around 43 HRC. Other metals can also be electroless plated but nickel is most commonly used.