ATVATP Prewound Trimmer head With Line For Stihl FS44 FS44R FS55 FS55C FS55R FS55RC FS56C FS56RC String Trimmer Replacement manufacturer part number: 25-2 Fits: STIHL 4002 710 2191 FS88 FS90(2005 On) FS 90R FS100 FS100R FS106 FS108 FS100R Uses .080" .095" or .105" line Thread size: 10mm x 1.0LHF Won't work on trimmers that use coarse thread size 10mm x 1.25LHF, otherwise you need an adapter for it