• Commercial string trimmers are used to cut through tough weeds and even brush, using a thin nylon string that whips through plant material very quickly. These trimmers are often powered by gasoline and oil mixtures or propane. Electric commercial string trimmers do exist, but the lower power of these models generally disqualifies them for heavy work.
  
  

Lehr Eco Trimmer

• The Lehr Eco Trimmer line includes four different propane-powered string trimmers that share the same basic features and downsides. The experts at ConsumerSearch say that propane-powered models eliminate the need for storing gasoline, produce much less pollution and have the same power of a gas model. The 25 cc engine and 17-inch cutting width makes them ideal for commercial use. Some of the models in this line feature exchangeable curved and straight shafts while others have adapters for attaching edgers and other attachments. The heavy weight and slight power loss when compared to other propane models are these models' only downsides.
  
  

Craftsman 79194

• With a 29 cc engine, this gas-fueled model has the power for commercial use. The 14-inch cutting swatch can't compare to models with a 17-inch width, says the ConsumerSearch website, but its split shaft system accepts a wide variety of attachments made by Craftsman, and it can be used as an edger, which may reduce the need for separate pieces of equipment. The cutting head is fixed, which causes less tangling but requires you to stop using the machine to replace dull strings. The spring-assisted starting system bypasses the difficult start-up process many other two-stroke gasoline string trimmers suffer from. The main problem with this model is its 19-lb. weight before any fuel is added. A shoulder strap should help prevent fatigue during hours worth of work.
  
  

Shindaiwa T2510

• The Shindaiwa is one of the most expensive commercial string trimmers available, but it is also one of the best. The Popular Mechanics review of this trimmer notes that it uses an unusual two- and four-stroke hybrid engine. It features the easier start-up process and smoother operation of a four-stroke engine, but it uses the traditional gas and oil mix of a two-stroke engine. It features plenty of power for the toughest landscaping and trimming jobs. Reloading new string is easy, but additional maintenance and problems may occur with the engine due to its combination of two very different systems.