Any piece of mecha equipment integrated into a mecha's hand slot-and only the hand slot-can be stowed magnetically against the mecha or in a storage compartment as a move action. This frees up the hand to perform more delicate manipulation (such as opening a door or pressing a button) or grabbing another piece of mecha equipment.
A mecha may have more pieces of equipment for its hand slots than it has hand slots available; it just can't use them all at once.