Non-prehensile tail
Non-prehensile tails are unable to grasp. However, they do serve an important purpose to help monkeys balance during movement. If you have seen videos of monkeys while they walk, you might notice that they sway their tails from one side to another to keep their balance, mainly while walking on tree branches.
While some non-prehensile tails are short, length is not always an indicator if a tail is prehensile or not. For example, the appropriately named long-tailed macaque (Macaca fascicularis), seen in the image to the right, does not have a prehensile tail.