One thing that has helped me when I do need to use nylon invisible threads is an old nylon knee-high stocking. Really. I cut a tube about 2 inches wide from one that had a small run in it (I used the part without the run). I then stretch that piece out a bit, much like a rubber band, and put it on the spool, also like putting a rubber band on something (slip it over it, pull it out a bit, cross the sides, then slip it over it again --- hope this makes sense). This provides just enough extra tension that the spool can then be used on either a vertical or horizontal spool pin without the problem of tightening and breakage or relaxing and coiling up under the spool or the bottom of the fabric. Some machines also now come with a little white netting tube that does essentially the same thing.