Helios, Hydros and Access all share the same basic fit criteria. Helios is a painted ferrule, while Hydros and Access are unpainted. Unlike some older technology, our ferrules on painted and non painted joints are exactly the same. We do NOT use glued in Spigot ferrules, because they do not transfer energy well. Instead the outside of the blank is precision ground to mate perfectly with its adjoining section. The only difference is Helios is ground slightly more to allow for the paint thickness. On a finished Hydros and Access rod, the unpainted gap space between sections is designed to be 1/2". The gap space has no bearing on the action of the rod, its is only for wear. The more a rod is put together, the tighter the gap spacing will become over a long period of time. If there was no gap to account for this, eventually the ferrule would become loose from wear. On the Helios this wear is taken into consideration as well, it is just not visible because the ferrule is painted.