You’ll need at least one block, fittings, tubing, radiator(s), coolant, cleaners, and a pump with some kind of pump top. While technically optional, a reservoir is highly recommended and can serve as the pump top with the right model. Distro plates can replace a traditional tube reservoir, as well. The fittings will need to be compatible with the type and size of tubing you’re using, and accessory fittings such as drain valves and pressure check valves are also highly recommended as safety precautions and maintenance aids.