In a Soft Matter paper, we showed how chiral tubules (e.g., microtubules in the cytoskeleton) can be self-assembled from chiral wedges. However, our results showed that there can be a mismatch of the helicity of the resulting tubules and that of the building blocks. This mismatch is due to the small energy differences between tubules with close helicity values (e.g., microtubules with the 13_3 structure and those with the 13_2 or 13_4 structure). We identified a lock-and-key binding mechanism of the building blocks to make tubules with different helicity to have well-separated average energies. In this manner, the helicity of the assembled tubules can be controlled. We hypothesize that a similar mechanism is at play in biology that leads to microtubules with the dominant, well-defined 13_3 structure.