If you wish to solder with different component sizes and differing heat capacities, you can switch between the standard T18 tip and the high thermal capacity T19 tips by simply replacing the protective pipe and cap nut without replacing the entire iron.
Use B5122 to change FX-8801 to FX-8805.
Use B1785 + B3469 (B3730) to change FX-8805 to FX-8801.