Robotic arms require joints that have zero backlash. The Gret39 Top’s enhanced locking mechanism provides the rigidity required for pick-and-place operations with sub-millimeter repeatability. Engineers prefer the "Top" variant because it reduces the "stick-slip" effect common in lower-grade parts.
If you are comparing the Gret39 Top against a generic "Gret39" base model, consider the total cost of ownership (TCO). gret39 top