Need brush cutter adapter for FS66 trimmer

[sofasurfer]

Looking for a brush cutter adapter and blade for FS66 trimmer. All the "universal" sets on line have splines in the adapter. My trimmer shaft has a "flat" on the shaft instead of splines. Can someone explain why I do not have splines. Do you know of any sites that have one with an affordable price? Thanks.

 

[Rivets]

Try this site. This is one time I highly recommend going through and double checking with a Stihl dealer, as if it doesn’t fit you should be able to return it. https://www.diyspareparts.com/parts/stihl/diagrams/fs-66/