The GreyT Telescope can be assembled in two different configurations, with each having a different way for running the string.
Like the name implies, the Internal String configuration runs the string through the center of the telescope. This gives the string more protection since it is inside the stages, and also leaves more room open around the telescope for other mechanisms.
The External String configuration runs the string outside the telescope. While this does not provide as much protection for the string, it does allow for easier assembly and maintenance of the system. Additionally, since the base stage sits lower in the flipped gearbox, this configuration also allows for longer stages, meaning more stroke for the same height telescope.