The Arc-Hand Block (bandalson makgi) is a block used in ITF-style taekwondo. WTF-style taekwondo has no block called an Arc-Hand Block, though the Boulder Push is similar.
The arc-hand can be executed from nearly every stance, though walking and x-stances are usually preferred. The palm usually faces the defender with the exception of a reverse block from a walking stance. The blocking tool reaches the same level as the defender's forehead at the moment of the block.