A string trimmer comprising a string trimmer head, the string trimmer head comprising: a spool including: a central section formed of a core wall around a core and passages extending through the core wall; an upper flange located at an upper portion of the central section; and a lower flange located at a lower section of the central section; an end cap inserted into an opening to the core, the end cap having a protrusion that extends from one side of the end cap to the other side of the end cap and includes a passageway that is aligned with the passages in the core wall; a top housing component connectable to a bottom housing component to form a spool housing surrounding the spool and to releasably engage the spool, wherein the spool housing is to rotate with the spool when engaged with the spool and to not rotate with the spool when disengaged from the spool, the spool housing including an eyelet through which a line wound around the spool is to extend; and a spring to control the releasable engagement between the spool housing and the spool, characterized in that: the spool is coupled to a drive member of the string trimmer and is to be continuously rotated with the rotation of the drive member around an axis, wherein the spool is continuously rotated with the rotation of the drive member when the spool housing is disengaged from the spool, and the spring is to bias the bottom housing component away from the spool. a spool including: a central section formed of a core wall around a core and passages extending through the core wall; an upper flange located at an upper portion of the central section; and a lower flange located at a lower section of the central section; a central section formed of a core wall around a core and passages extending through the core wall; an upper flange located at an upper portion of the central section; and a lower flange located at a lower section of the central section; an end cap inserted into an opening to the core, the end cap having a protrusion that extends from one side of the end cap to the other side of the end cap and includes a passageway that is aligned with the passages in the core wall; a top housing component connectable to a bottom housing component to form a spool housing surrounding the spool and to releasably engage the spool, wherein the spool housing is to rotate with the spool when engaged with the spool and to not rotate with the spool when disengaged from the spool, the spool housing including an eyelet through which a line wound around the spool is to extend; and a spring to control the releasable engagement between the spool housing and the spool, characterized in that: the spool is coupled to a drive member of the string trimmer and is to be continuously rotated with the rotation of the drive member around an axis, wherein the spool is continuously rotated with the rotation of the drive member when the spool housing is disengaged from the spool, and the spring is to bias the bottom housing component away from the spool. the spool is coupled to a drive member of the string trimmer and is to be continuously rotated with the rotation of the drive member around an axis, wherein the spool is continuously rotated with the rotation of the drive member when the spool housing is disengaged from the spool, and the spring is to bias the bottom housing component away from the spool.