Specs: Description: Hybrid Trimmer Head, Arbor Sizes: M8 x 1.25 LH x 22 mm stamped #1 screw, M10 x 1.25 LH x 21 mm stamped #2 screw, M7 x 1.00 LH x 22 mm stamped #3 screw, M8 x 1.25 RH x 22 mm stamped #4 screw, 5/16"-18 UNC RH x 19 mm stamped #5 screw, M8 x 1.25 RH stamped A nut, M10 x 1.25 LH stamped B nut, M10 x 1.00 LH stamped C nut, 3/8"-24 UNF-2B RH stamped D nut, 5/16"-24 UNF-2B RH stamped E nut, M10 x 1.50 LH stamped F nut, M8 x 1.25 RH stamped J nut, 3/8"-24 UNF-2B LH stamped K nut. Compatible With/Replacement For: most gas, straight and curved shaft trimmers. Stens 1 year warranty ensures reliability and performance for every part. Stens branded parts are trusted by professional dealers to perform OEM quality repairs. Compatible with/Replacement for Arrowhead OEMs: 385-853