An assembly for use with a trimmer, a trimmer head, a method of operating an assembly for use with a trimmer, and a flail cutter assembly. The assembly may include a trimmer head including a body couplable to a drive shaft of the trimmer, the body being rotatable about an axis and defining an annular channel； an attachment including an attachment body extending about the axis and positionable in the channel and an attachment operation member projecting radially from the attachment body； and a retainer radially movable between a retaining position, in which the retainer overlaps the channel to selectively retain the attachment when the attachment is supported on the body, and a release position, in which relative axial movement of the attachment and the head is allowed.
