Sarah Pitt advertises in the Virginia Gazette in October of 1768 that she offers for sale "a great assortment of threads".  Some of the threads likely available were what we like to call "Tailor's" threads.  The  30/3 "Tailor's" Thread is a weight often found being used for construction in tailored garments, and likewise in some of the more stressed areas in gown making, such as in the pleating of the skirts.  

• Wonderful for buttonholes.
• These small spools are perfect for individual projects with 20 meters/65 feet.
• 30/3 "Tailor's" thread is available in Natural & White