Blade Friction Washer. NB if it doesn't say GENUINE then it probably isn't.
Genuine Mountfield Petrol Lawnmower Handle Locking Lever Part No.381003253/0
Genuine Mountfield Petrol Lawnmower Rear Roller Bearing Part No.119216036/0
Genuine Mountfield Petrol Lawnmower Pinion Gear, Part No. - 122570125/0
Genuine Mountfield RM55 Lawnmower Engine Oil Seal Part No. 118550379/0
Genuine Mountfield SP425 Lawnmower Wheel Part No.381007448/1
Genuine Mountfield Stiga Lawnmower 46cm Mulch Blade 181004460/0 S46 S461 UT41
