Compatibility notes
Find the line specified for your trimmer head. Then compare the reel length, profile and pack price.
Find the machine reference
Use the exact trimmer and head model. The brand alone is not enough to choose a spool.
Read the diameter
Match the permitted diameter in the manual, in millimetres. Do not assume thicker line is an upgrade.
Separate the pack types
Loose line, a wound spool and a complete head are different purchases. Compare like packs.