do a 'tug test' to see if it is strong thread- if it does not 'readily' break when a piece is held between your 2 hands and given a tug it is usually strong enough for piecing. I know some people don't want to use thread that says 'serger thread' on it - but I have successfully used literally hundreds of cones of serger thread- my mother bought a whole *going out of business* inventory of serger thread one time & we spent years using up all those cones ~ the thread worked fine for piecing and was even good on the long-arm with the high speeds that many threads do not handle. we did have a few cones that were 'weak' did not handle a strength test- we did not use those for piecing/quilting. those were set aside for serging or embroidery that uses many threads to make up the design.