It's very possible this thread guide does NOT go with the machine. I've received many attachments with vintage machines that don't go with the machine. Whoever is clearing out grannies just sticks everything in the box that they find that's sewing related....it doesn't fit either the FW or 301 because it fits a different machine, probably. The felt guide would protect the finish from scratching.
You really shouldn't need a seam guide on the 301.