A trimmer head assembly has a housing that defines an interior. A spool is provided. The spool can be inserted into the interior of the housing either in an upright configuration or in a flipped inverted orientation. A spring is provided in the housing that biases the spool into a first position within the housing. A ratcheting mechanism exists between the spool and the housing that enables the spool to rotate only in a first direction when in said first position. The direction of rotation permitted by the ratcheting mechanism depends upon the orientation of the spool within the housing. In this manner, a single trimmer head assembly can be made to operate on a clockwise trimmer or a counterclockwise trimmer merely by inverting the spool.
