21FS 500, FS 550
English / USA
Grass Shield
*
: The grass shield may only be used 
together with the 2.4 in (60 mm) 
diameter thrust plate (A) and the 
deflector for mowing heads.
* see "Guide to Using this Manual"
STIHL AutoCut
STIHL TrimCut
: Block the output shaft with the stop 
pin.
: Screw cutting head 
counterclockwise onto the output 
shaft (7) and
Important: Remove the stop pin.
Removing the mowing head
: Block the output shaft.
: Unscrew the mowing head 
clockwise.
STIHL PolyCut 40-3
: Block the output shaft with the stop 
pin.
: Position the mowing head on the 
shaft.
: Fit the 2.4 in (60 mm) diameter 
thrust washer (6) –
convex side must face down.
: Screw on nut (4) counterclockwise 
and tighten down firmly.
Important: Remove the stop pin.
Removing the mowing head
: Block the output shaft.
: Unscrew the nut clockwise.
If the mounting nut is too loose (cannot 
be tightened properly), fit a new one.
A
398BA052 KN
7
398BA053 KN
4
6
398BA054 KN