The best quality basic thread is made from long staple Egyptian cotton. Many threads are made by twisting the ends of left over pieces of thread together. That makes it weaker and cheaper to make. If you look at thread closely and can see flubs then don't use it in your high end machines. The older vintage machines didn't mind flubs or lint. The thread guides were outside so most of the lint was taken away in the air not enclosed guides like the newer machines.