a trimmer head wherein the driveline of the power tool is connected to a core member . a spool is mounted to the core member and directly driven by the core member . a housing is mounted for axially sliding on the core member and a spring urges axial movement of the housing relative to the core member . interlocking structure on the spool and housing produces interlocking for common rotation of the spool and housing responsive to urging by the spring . release of the interlocking structure is affected by opposing said spring urging . desirable additional features include selective alternate positioning of the spring for automatic and manual only release of said interlocking and a line loading assist provided by a tubular post through the spool alignable with housing eyelets for threading line through the eyelets and spool and winding thereof onto the spool by manual turning of the spool relative to the housing .