Spintronic devices operating with pure spin currents represent a new paradigm in nanoelectronics, with higher energy eﬃciency and lower dissipation as compared to charge currents. This technology, however, will be viable only if the amount of spin current diﬀusing in a nanochannel can be tuned on demand while guaranteeing electrical compatibility with other device elements, to which it should be integrated in high-density three-dimensional architectures. Here, we address these two crucial milestones and demonstrate that pure spin currents can eﬀectively propagate in metallic nanochannels with a three-dimensional curved geometry. Remarkably, the geometric design of the nanochannels can be used to reach an independent tuning of spin transport and charge transport characteristics. These results put the foundation for the design of eﬃcient pure spin current based electronics, which can be integrated in complex three-dimensional architectures.