The original metal fan on 70-71 240Z's wasn't the best idea Datsun had. The heavy fan caused premature wear on water pumps, and if the pump broke could cause significantly more radiator damage. This kit includes a new fan clutch, and a new plastic fan (from the 72-73 240Z) to replace the original early metal fan.
These parts are available separately for 72-73 240Z's. If you have a 72 or 73 and need both, you can just choose this kit as well.