In order to save money and time with your gas lawn trimmer, learn how to rewind the string onto the spool so it unwinds in the most efficient way. This will enable you to buy string in 1000-yard lots and attach it yourself to the spool. Be sure to purchase a replacement spool as your first one has a lifespan of about three years, after which time the hardware or garden center may no longer carry that model.
Step 1 - Remove the Spool from the Trimmer
Remove the spool by unfastening any screws that hold the spool axle in place. If it is self-attached, push it down while twisting counterclockwise or pull it off through the bottom of the drive shaft.
Step 2 - Rewind the Existing String
Check that the string is fastened through the opening in the spool center. At least one inch of string should appear through this hole. Wind the string clockwise onto the spool, ensuring that the rows of string do not overlap each other but are exactly parallel to each other, snugly aligned with each previous strand all the way around the spool, and perpendicular to the spool's long axis. When you turn the string to wind it down the long axis of the spool for the next layer, ensure that each new turn of string lands exactly on top of its counterpart on the layer below.
Step 3 - Fill the Spool and Reinsert it Into the Trimmer
Continue placing the string onto the spool until you have filled the spool just below its end flange. Insert the last inch or two of string through the guide hole on the trimmer. Reinsert the string spool into the trimmer by pushing it directly, or lifting and turning it to fit into the guide slots. Rescrew the spool guide axle into place if needed.
Step 4 - When to Replace the String and/or the Spool
When the string of your lawn trimmer becomes worn or knotted, you will need to replace it on the spool. Remove the spool device from the lawn trimmer as described in Step 1. Examine the spool to see that the interior is still at 90 degrees to the flanged ends, and that the flanges are not bent, chipped or corroded. If the spool is damaged in any way, replace it with the second spool you bought when purchasing extra string for your trimmer. A misaligned or damaged spool could cause injury to the lawn trimmer user.
Step 5 - Measure and Cut New String
Cut 50 yards of new string for the trimmer. Insert one inch of the string into the guide hole in the center of the spool. Rotate the spool so the string is wound snugly onto the spool in parallel strands that run exactly perpendicular to the long axis of the spool. When the spool is full, run the last few inches of the string through the guide on the trimmer and reattach the spool.