How do I advance the spool of the trimmer's string? Your trimmer is equipped with an auto advance system that will feed more string as you trim. Bumping the head of the trimmer in an attempt to manually bump feed string can cause damage to the unit and is not recommended. Related articles What type of string does this trimmer use? How should I store my trimmer when not in use? My SJH904E Hedge Trimmer isn't operating properly, what do I do? What is the maximum depth my TJ599E unit can cultivate? What are the best uses for the Heat Gun attachments?