Square Shaft (SS) / Round Shaft (RS) Extensions
Plain extensions, either square or round, are added in standard lengths of 3, 5, 7 and 10 feet until the lead section penetrates into the bearing strata. Typically, square shaft extensions can be used in both compression and tension applications. Round shafts are more commonly used for compression and have a greater section modulus, resisting bending in weaker soils.