This might be a noob question. . . but I am a Stihl tool noob. I just inherited several Stihl FS weed trimmers, FS94R, FS130, FS110R, and FS131R. They all need work but I'm sure i can get them working. Are all of these designed to safely use the brush knife or grass cutting blade? And what about the hedgetrimmer attachment? I was told if they don't have a solid shaft they won't be able to handle these different attachments. that doesn't sound right to me. Thanks for your guidance.