Will Expand-it attachments from a Toro string trimmer fit a Troy Built Trimmer?

Yes, unless you have an older Homelite from the late 90's, all of the expand-it attachments are universal, which, in my opinion, makes the expand-it a very attractive option. The attachments fit Toro, Ryobi, Poulon, Homelite, Troy-Bilt, Huskqvarna, etc.