When connecting two different types of metallic pipes, what is used in between?

When connecting two different types of metallic pipes, a dielectric kit or fitting is utilized to prevent galvanic corrosion. This type of corrosion can occur when two dissimilar metals come into contact with each other in the presence of an electrolyte, such as water. The dielectric fitting acts as an insulating barrier, ensuring that the two metals do not directly connect, thereby preventing electrical current from flowing between them which could lead to deterioration of one or both pipes over time.

Using a dielectric fitting is essential in plumbing and heating systems to maintain both the integrity of the piping and the quality of the water being transported. Other options, such as a rubber gasket, metal coupler, or cement, do not provide the same protective insulation against galvanic corrosion that a dielectric fitting does.