The ECT phantoms are pre-assembled prior to packaging with the exception of the cold spheres. The set of spheres (6) are located within the cylinder, the spheres are mounted in the cylinder by gently screwing the bottom of the spheres into threads located on the bottom of the cylinder. Inside the cylinder when looking at the cold rod insert you will see the top plate and six pie shaped sections of cold rods. Between each section is a row of vacant holes. The spheres are inserted into the third vacant hole, which should line up with the threads on the bottom of the cylinder. For most users the largest sphere is set counter-clock wise from largest pie section. Gently screw the remainder of the spheres in the threads (going counter-clock wise) with the next size down to the smallest spheres next to each pie section.