This replacement oil pump piston (pump piston), in practice often also called the oil pump worm, is a precisely made component of the chain lubrication system (oil pump) on professional-class STIHL chainsaws. Its basic technical role is the axial-rotary pushing and constant metering of oil from the tank towards the guide bar and the saw chain. The part is driven via the clutch and the crankshaft, and thanks to the worm thread it ensures an even flow of oil proportional to the engine speed. Fitting this quality replacement part by the manufacturer DR, which fully follows the factory dimensional specifications, ensures reliable lubrication of the cutting tool and prevents overheating of the bar during intensive work. During an overhaul of the lubrication system and installation of a new pump worm, it is necessary to completely dismantle the clutch and sprocket cover assembly. Thoroughly clean the pump seat and the inside of the housing of the mixture of crusted sawdust, resin and old oil, because the presence of small impurities can block the operation of the spindle and lead to rapid failure of the new part. Before fitting, lubricate the piston generously with clean oil or a dedicated grease. During installation, pay attention to the condition of the sealing rings (O-rings) in order to prevent loss of pressure and oil leaking inside the clutch area. Key features Part type: High-compatibility aftermarket part Manufacturer: DR Catalogue number (OEM): 1135 647 0600 (11356470600) Installation position: Oil pump mechanism near the clutch (Oil pump, Clutch) Function: Rotary-thrust worm piston for metering chain oil Material: Reinforced metal alloy resistant to mechanical friction and wear Unit of measure: Sold per piece Compatible models STIHL chainsaws STIHL MS 341 STIHL MS 361, MS 361 C STIHL MS 362, MS 362 C-M STIHL MS 363.0 STIHL MS 400.1 C-M