Probably the piton with the shortest and most easily remembered name ever - the U by Petzl is designed for somewhat wider cracks in the rock. It is simply perfect for both limestone and granite. Soft steel hooks adapt to the structure of the crack without effort. However, theres a catch: in general, these hooks are harder to remove from the rock and cant be used as often as hard steel hooks. The U by Petzl is a type P angle piton, which means that the UIAA has only approved it for progression on technical climbs.