Use any line you like, but keep to the original diameter which should poke into the holes on the spool.
Look for rotation arrows which tell you which way to wind the line!
John
my neighbour who borrows my ryobi strimmer was grateful as i off course wanted nothing in return so he bought me some strimmer cord on monday as it was running low
the spool was about 5 year old and held 5m crudely wound
when the line arrived at my bench, it was 100m long so i plan to live to 170 year old to show thanks
it was 1/16th" or 1.6mm and was between £5 and £10 from amazon
My (Makita) strimmer goes through line for fun. Mainly because we have lawn up to the fence and I'm always try to kill weeds that try to grow up the fence posts.