This disclosure provides a tool or an apparatus that can be held and operated with one hand to attach a corner bead to an outside corner of drywall. In one example, the tool includes a frame, a pair of contact surfaces rigidly coupled to the frame, a handle pivotally attached to the frame, a pair of stapler units rigidly coupled to the frame, and a linkage mechanism comprising a pair of transmission arms and mechanically coupling the handle to the stapler units for translating a force displacing the handle from a first position into a controlled motion of the transmission arms, thereby triggering the stapler units to release fastening pieces.