The Cold Fusion Nucleus was the successor to the orginal Cold Fusion line of yo-yos by Playmaxx/ProYo. As with the Isotope-1 and Isotope-2 yo-yos, the Nucleus featured a slimline Butterfly body profile. In addition, they added O-rings behind the spacers, allowing the user to adjust the string gap by twisting the body halves. This setup can also be seen in Duncan yo-yos such as the Freehand 2 and the first release model of the FHZ.