• Auto-feed string trimmers use centrifugal force to release trimmer line. Each time the unit is activated, the spinning of the trimmer head exerts a force that unlocks the trimmer spool, allowing line to be released. A spring-loaded mechanism relocks the line after approximately 0.25” of line has been release. Therefore, every trigger pull will release line.
• Bump feed/ bump and feed string trimmers work with a similar mechanism, but the spool lock is manual disengaged by the user by “bumping” the trimmer head on the ground while the unit is in use. This mechanism provides operators with more control over how much line is used. 

For attachment capable string trimmers, the following brands are compatible:
GPoulan Pro, Ryobi-Expand-it and Trimmer plus.
If you are unsure if you have an attachment capable string trimmer unit, please contact us at info@greenworkstools.com. 

Trimmer line will break off during use which is a normal occurrence. In harsher terrain or when used to edge the string trimmer's line will break off more often as it makes contact with hard surfaces. To reduce line breakage here are some tips:

• Keep the underside of the trimmer head/guard area clean of debris.
• Ensure that the cutting blade is clean/clear, and the blade is exposed and shard enough to trim the line. This will also help to reduce excessive line breakage.
• Avoid direct contact with hard surface areas when using the string trimmer.
• In thicker, denser, and longer grass, you may want to go slower. Listen to the sound of the string trimmer, if it reduces speeds, or slows down too much, back away from the grass and start again at a slower pace.