I just made a spooler to help wrap cutter line onto my new automatic string
feed grass trimmer ("weed eater" type of device). I used serrated line
instead of round line as they plainly state is required. It worked great
anyway.

The spooler is simply a bit which fits into the center of the empty spool
and then into my cordless drill. The spooler bit has to be soft enough to
avoid damaging the spool, and it has to be made well enough so the spool
turns without wobbling a lot. I made it out of a short wood dowel and a
bolt, held together with super glue. As the spooler slowly turns in the
specially made drill bit, the line is very neatly wrapped around the spool.