I own a 4 cycle TroyBilt 525 trimmer with a "yellow" head ... original from the store. I can never seem to string the line correctly and the manual is all eaten up. Their website sucks so I am turning to this group in desperation! It is the "bump" style with a screw off top. My problem is after I wrap the string, I can't figure out how to get it through the two holes and have the bob sit properly.... thinking of goin to the fixed type of hard edges strings but have heard stories of them breaking off and flying around and cutting you pretty bad ... any advice would be greatly appreciated.