HIPA 8mm x 1.25 LHM Trimmer Head for STIHL FS50 FS51 FS51AVE FS55R FS60 FS61 FS61AE FS61E FS65 FS90 FS90AVE FS91 FS96 String Trimmer Arbor size: 8mm x 1.25 LHM Ideal for consumer and commercial use Simple, problem-free indexing mechanism