From a QN Member: Most regular sewing thread used for seam construction is generally a 50wt thread not a 40wt. And a size 80 needle is generally used for this weight thread though some applications require a 90(needle). 40wt thread is generally used for machine quilting or machine embroidery. And most sewing machine’s needle threaders will not work with a size 70 needle . . Look at the size of your own sewing threads. Coats and Clark’s regular thread is 50wt, Aurifil is 50wt, Mettler general sewing thread, Gutterman is 50wt as well as many other of the common manufacturers.
From Schmetz Needles: What Needle Size Do I Use
The most popular thread used for all types of sewing, quilting, and
crafting is a 40 weight thread. When using a 40 weight thread, use
a size 80/12 needle.
If using a thread finer than a 40 weight, such as a 50 weight, use a
smaller needle size such as 70/10. Likewise, if using a 30 weight
thread, use a needle size larger than 80/20, such as 90/14 or larger.