The Double Clawshots, simply Clawshots in Skyward Sword, are an item in Twilight Princess and Skyward Sword.
In Twilight Princess, Link obtains his second Clawshot in the seventh dungeon of the game, the City in the Sky. After defeating the mini-boss of the dungeon, an Aeralfos, he can open a chest and find another Clawshot. Combined with the one he found in the Lakebed Temple, he creates the Double Clawshots.
The Double Clawshots allow Link to grapple to targets, and then upon hooking to one, Link can aim around with his other Clawshot to grapple to another target. Link can also use it to attack enemies, grab treasures and Rupees, and break pots and other various objects. This item is required for stage two of the STAR Game, and to complete most of the later dungeons of the game, including the City in the Sky and Palace of Twilight.
Double Clawshots icon from Twilight Princess HD
In Skyward Sword, Link obtains the Clawshots as a pair on completing the Lanayru Province Silent Realm. One of the four gifts of the Goddess, they can cling to only targets and vine walls.
They are used to reach the Lanayru Sand Sea, search the Sandship, and eventually find Nayru's Flame.