Double line, for cutting and thinning. The nylon line is fed by tapping the cutting head on the ground. Comes standard on many trimmers.
Adaptor bolts available to fit most of brush cutter, Bolts size is following:
10 x 1.25mm FLH
10 x 1.25mm MLH
8.0 x 1.25mm FLH
8.0 x 1.25mm MLH
7.0 x 1.00mm MLH
3/8 x 24 FRH