An apparatus for forming a first component making up at least a part of a housing on a trimmer head and a method of using the apparatus. The housing has a rotary axis and is configured to support at least one radially projecting cutting component. The first component has a central axis. A forming unit defines at least one cavity within which a moldable material is confined to produce at least a part of a wall on the first component that extends around the rotary axis. The forming unit is configured to allow selective controlling of a quantity of a moldable material introduced into a first discrete subvolume at a first location in the one cavity to thereby allow selective controlling of a mass of a portion of the at least part of the wall formed by the moldable material in the one cavity at the first location to facilitate dynamic balancing of the housing, within which the first component is incorporated, with respect to the rotary axis.