Connecting Threads: Essential is 50 wt 3 ply
Essential Pro is 70wt 3 ply poly
The Pro is excellent for bobbins when piecing. It adds less bulk to the seam. There is a lot to know about thread. I use to think just pick a color and that was all. The best education you can get about thread is on Superior Thread website. The DVD of Thread Therapy has all the info you need to be a thread expert.