Alice, most hand quilting thread is coated to prevent tangles and ease of use. This thread is not recommended for use in a sewing machine.
Regular thread, is usually 50wt. This is the common thread you will find made for sewing, but not all 50wt or regular thread is created equal. For garment construction, using a basic Coats and Clark sewing thread is fine, but I would caution against using in piecing blocks for a quilt. This type of thread has a polyester core, therefore, will be stronger than the 100% cotton fabric we use in quilt tops. While this may sound like a good thing, it can cause problems of fabric cutting or ripping along a seam line making it imposible to mend. It is a better idea to use a 100% cotton thread on a 100% cotton fabric. This thread will break with stress before your fabric does. A lesson I learned the hard way.
Quilting by machine offers many options, from a thin invisible type thread to a bold thick 12wt. decorative thread. You may want something to bury itself if doing a stitch in the ditch method of quilting, something more bold for decorative quilting. The possibilities are endless. Some use a very thin 70wt. thread with a thin machine needle to do tight stippling. This allows the background to recede and elements of the block to pop forward on a quilt.
I hope this is helpful in a small way. Once you become familar with the different types of thread, your decisions will be based on what gives you the desired effect. Thank you for your question.