<!-- from fixya rte -->How to restring Troy Built weed eater - Troy-Bilt 4-Cycle Curve Shaft Gas String Trimmer #41ADT41C966

SOURCE: troy built weed eater won't feed line

Check the size of the line,(OD), make sure you are using the correct size, sometimes cheap line will be problematic, also, you said you are re-stringing it, try a new batch of string, the old string inside the hub can get chaffed and will stick to itself...

SOURCE: Fuel line size for troy built TB20CS weed eater

You probably have found the solution by now I would assume... TB won't tell you this because they want you to buy their stuff..
You probably are looking at the 0.08" diameter that's just a bit smaller than the 3/32". Hope this helps....

SOURCE: The head will not spin on Troy Built weed eatter

sounds like your flex cable has taken a trip south. Pull the shaft off the head and take a look at the flex cable. If flex cable is ok, they your clutch is defective.

SOURCE: Tryingto replace my troy built weed eater's head

clean grass off between shaft and the top of the head. hold weed eater still and turn the head, looking between the shaft and the top of the head. There will be what looks like a hole. Place something there that will keep the shaft from turning, then twist the head off.