This is a Stihl AutoCut 27-2 trimmer head, identified by its part number 4002 820 2302.It is designed for brushcutters and trimmers, including models like the FS 55, FS 56, FS 91, and FS 111.The head features a semi-automatic tapping mechanism to feed the line while in operation.It supports a 2.4 mm (0.095 in) trimmer line diameter.