This original STIHL gear set (bevel and crown wheel gears) is the heart of the angle gearbox (head) of your trimmer, responsible for transmitting and converting torque from the drive shaft directly to the head with line or blade. Made of specially hardened and case-hardened steel, these gears are designed to withstand extreme centrifugal forces, high temperatures and constant impacts when mowing dense vegetation. By choosing the original STIHL set, you get perfect factory meshing, which eliminates increased vibration, overheating of the head and premature chipping of the teeth, the main flaw of cheap replacement gears. Replacing the gear set requires expert and meticulous assembly inside the aluminium housing of the trimmer head. Before fitting, the inside of the housing must be completely cleaned of old shavings, broken teeth and contaminated grease. Be sure to check the condition of the bearings and sealing oil seals – if they have play or leak, replace them so that the new gears do not become unbalanced. After successful assembly, be sure to fill the angle gearbox with the dedicated STIHL grease for gearheads and regularly check its level during the season to prevent dry running and accelerated wear. Key characteristics Part type: Angle gearbox gear set (bevel–crown wheel pair) Manufacturer: STIHL Material: High-quality heat-treated tool steel Catalogue number: 4117 640 7300 (4117-640-7300) Compatible models Trimmers and backpack brush cutters (older series with the stated chassis number/year): STIHL FS 80 (older models of the 4112 series: E, RE, AVE, AVRE) STIHL FS 81 / FS 86 STIHL FS 90 (older 4117 series) / FS 96 STIHL FS 106 / FS 108 / FR 106 / FR 108 STIHL FS 160 / FS 180 (for models with a gearhead up to production number 3 50 609 047)