This Stens Silver Streak Ninja Trimmer Line features a round shape and is highly durable when contacting concrete, landscape rocks and trees. This general-purpose trimmer line is a good choice for a variety of medium-duty trimming jobs around the yard because of its versatility. Stens has added extra durability to its Ninja trimmer line with a robust coextruded design, featuring a core protected by an outer shell. The co-extruded design holds up better in situations when the trimmer line contacts concrete and other hard surfaces. The co-extruded design of this trimmer line significantly reduces breakage to the line from contact with hardscape surfaces. Ninja delivers better results and lasts longer than many competitive types of trimmer line.