Stihl FS 90 Trimmer, Installing a Blade .In the video I remove the string head off the Stihl FS90 trimmer and install a blade.I also talk a little about different types of trimmer string.. I use the tools that Stihl provides with the FS90 Trimmer,You can also use other tools to remove the string head or bump feed and install a blade.You may need to purchase a nut ,washer and bump guard if you do not already have them. Most straight shaft trimmers have left hand threads to hold on the blade or string head. In the video I remove a guard but you should never remove safety equipment and run the machine. You should also wear safety glasses.