The quick lock trimmer head from DR is compatible with all current DR TR4 wheeled trimmers. The quick lock head allows you to quickly change the cutting cord without using any tools. All sizes of DR line can be used with this head, including the sawtooth 5.5mm. The locking mechanism securely holds the line in place so it won\'t get pulled out even when cutting thick weeds and brush. Includes 8 pre-cut pieces of 4mm green, 4.5mm blue and 5.5mm sawtooth nylon line. Please note: The quick lock trimmer head is NOT compatible with pre 2013 models. It is for current DR TR4 wheeled trimmers only.