PSS Shaft Seal 2-1/2" Shaft 4" Tube. Shaft Diameter: 2-1/2". Stern Tube Diameter (D): 4". Total Length (A): 9.625". Total Length (compressed) (Compressed A): 8.375". Rotor Diameter (B): 4.2". Carbon Cuff Diameter (C): 3.75". Stern Cuff Length (E): 2". The PSS Shaft Seal is the number one selling marine mechanical seal. worldwide and is installed as standard equipment by many of the worlds most. reputable boat builders / yards. The PSS Shaft Seal is also recognized as. the premiere retrofit (afte