A propeller system for an aircraft includes a propeller assembly rotatable about a central axis and a reduction gearbox operably connected to the propeller assembly via a propeller shaft. The rollers bear against both faces of the slit metal sheet and straddle the slits, all to reduce distortion caused by the knives and to iron out burrs. Additionally, an extended housing is provided on the housing so that the top of the extended housing is higher than the location of the operation part.