Product review (5 stars): Ryobi Replacament Bump Knob
This replacement bump knob was exactly what I needed to get my weed-eater working again.  My local stores have stopped carrying this unit and no parts are available locally.  It is a OEM part and I thought the price was really reasonable.  The seller listed all necessary information. My purchase was made very easy.

I highly recommend buying only the part(s) you need if your equipment is in good condition and it will be the most economical way to get it back in operation.