the numbers on a spool of thread are your (keys)
if your thread says---- 50/3 it is a 50 wt thread made with 3 plys-
if it says 40/2 it is a 40 wt thread with 2 plys---the higher the number the thinner/finer the thread-
12 wt thread is alot like string- 100wt thread is very fine (generally silk)
the ply is the number of (threads) spun together to create the thread- generally 2 or 3- but sometimes more or less
generally we use 40 or 50 wt thread for most piecing/quilting applications-
60 wt is often used as a bobbin thread.
visit Superior Threads- they have FREE charts you can print off which tell you the differences in the threads- the sizes/weights- the needles to use with each thread- and what they are generally used for- it is a very good resource- they have alot of invaluable resources - including Thread University.
I use Coats & Clarks Dual Duty Poly covered Poly. My mother always used C & C and my Great Aunt who died 15 years ago at the age of 93 and who was my quilting mentor only used C & C. I don't have any problems with it in my Janome. I clean out my bobbin case routinely to remove the lint. I have used Gutermann and Sulky if I am wanting to use a variagated thread or C & C doesn't have the color I am looking for. Thread is a machine and personal preference.
I have had 3 brothers,they don't care gutterman, C & C, mettler, sulky, connecting threads. Just make sure its the same in bobbin and top. That is the key with thread. The size should be on the end of the spools it should look something like 50/3(50 weight 3 ply). I wouldn't use lower than a 50 to piece. What I did in the beginning was write down my thread type and tension settings and kind of keep like a journal, it really helped me to get to know the ins and outs of my machine. A machine should be able to use most threads unless they are hand quilting or really thick you might need to really loosen your settings or have a special bobbin case. You machine should be able to use any thread. I haven't had a picky brother yet
50 wt 2 ply is thinner then 50w 3 ply. These are the common sizes for piecing. Lower sizes means thicker thread and they are best for machine quilting when you want the stitches to show. Very thin thread 60w and higher is great for bobbins and for machine quilting when you want the stitches to sink into the fabric and many use the thin thread for piecing. Example: Aurifil cotton 50w is 2 ply. Connecting Thread Essential cotton thread is 50w 3 ply.
For 50w 2 ply and higher weight thread you need a small size needle, I use size 80 or 70. 50w 3 ply thread is generally used with a 90/14 size needle.
Thread is an education all in itself. Here is a good place to start and also a great brand to buy to start learning about thread: http://www.superiorthreads.com/media...HOME_12-11.pdf
I have several different machines but for the most part I only use one thread; Aurifil. It is only 2ply, 50wt but very strong and very low lint to mess up your machine. For piecing I normally use either a natural or beige or tan color no matter what the fabric is. That's the nice thing about piecing; you don't have to match the thread to the fabric like you do when making clothes. I also like the Aurifil when doing hand applique; it hides in the fabric very well.
There us good info at Marathon thread. There are differnt weight & uses. For piecing 50wt/3ply or 50wt/2ply works very well. Thicker thread takes up more room thus altering your 1/4" seam. For decorating/quilting depends on project. I uses lots of embroidery thread-rayon- metallic & poly when doing decorative stitches on candlemats/tabletopper. (I make lots, I do craft shows I have Brother, Viking Janome Singer & Elna & don't seem to have problems even with C & C or metallics.
Check out all the information available at Superior Threads website. www.superiorthreads.com. I use their Masterpiece thread for piecing, they have great variegated colors and a wide variety of weights. Don't let your creativity be limited by just what you see at LQS or Joanns. Don't represent them just like their thread.