Square vs. Round Trimmer Line

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Homeowners and professionals have an opportunity to buy many different kinds of trimmer line. These lines come in a plethora of shapes and sizes; picking the one that's best suited for your model and your needs can get complicated.

When deciding whether to use square or round trimmer line, you should always refer to your owner's manual for size and line recommendations before making any purchases.


With four sharp edges, square trimmer line cuts faster and more efficiently. The square-edged line works well if you have tall, thick and heavy patches of weeds. The downside to square line is it breaks off quicker when it contacts stones, fences, curbs and buildings. Square line also has a tendency to jam in the spool retainer if the line isn't replaced properly.


Round trimmer line is smooth and will wear down less quickly. Most cutting occurs at the very tip of the line, so when round line contacts hard surfaces, like sidewalks or trees, it will break off less. The round line is also simpler to load into the spool retainer during line replacement, which may save time in the long run if you have a lot to trim.


The star or five-sided line uses this shape to make cutting even faster. Again, the same rules apply with the square model string: quicker cutting but faster wear.


All of the lines come in a wide variety of diameters. Industry standard on most models is .080 millimetres. This diameter measures the thickness of the line. If you're having problems with the square line breaking too quickly, you may increase the diameter size one increment. If, on the other hand, your line is jamming or fusing together inside the spool retainer, you can reduce the line size by one notch. Check with your owner's manual for maximum line diameter; overloading can damage the driveshaft.


Square trimmer line is quite similar to round trimmer line, and it really comes down to preference and feel. Their difference lies in the amount they will wear out. Consider how much you need to use the trimmer, over what physical conditions, how long each job will take you and how often you will need to replace your line. Both lines are relatively inexpensive, so you can experiment for the best results.