Killark AF-50AL - Copper free aluminum casted body and end coupling - Includes type "A" phenolic insulating bushing - PTFE synthetic fiber reinforced gasket with steel washer to help maintain a strong seal - Tinned braided copper ring - Rain, water and concretetight AF Series Expansion fittings are for use with IMC or rigid conduit installations. The AF Series prevents damage of the electrical installations typically used in buildings and bridges by compensating linear movement due to temperature fluctuation or structural movement. This series provides maximum 4” conduit movement (2” in either direction).