Wonder why when using machine thread to hand sew, it turns weirdly? It’s the twist!
So, it turns out that threads come in two flavors: S twist and Z twist
Machine threads are in Z twist, whereas hand sewing threads have a S twist. This convention is born out of the fact that the direction of the twist makes for an easy passage in the sewing machine, preventing the thread from…untwisting (you don’t say) as it goes through the various bibs and bobs, such as tension disks. In addition, the progress of sewing increases the twist of the thread, increasing its strength.
You may also find S twist threads referred to as “right twist” and Z twist as “left twist”. As far as I know, this refers to the direction of the spinning wheel when yarn is created, but this may be purely apocryphal, as I have also read that the naming may actually refer to the direction of the twist, no mention of spinning wheels (for the science nerds: right and left twist refer to the direction of rotation relative to the traveling of the thread, so using the right hand rule we have the thumb indicating the direction of the thread, and whether is curls clockwise or counterclockwise gives you the twist of the thread). If you are shopping from Japanese makers, here Z twist is referred to as left wrist (左撚り) and S twist as right twist (右撚り). In my experience most threads used for hand sewing are generally clearly marked with 手縫い糸.
I have also discovered that the buttonhole threads – at least the silk ones, which I would associate with hand worked buttonholes, and the only one I use now that I’ve become a hand worked buttonhole making machine – are in Z twist. I have not managed to find the reason why, so if you know, please let me know! As a consequence of the twist, one must wrap the thread around the needle clockwise I’m order to make an attractive buttonhole, and procede from right to left. This notion I have comes back to my embroidery days, as I remember reading that S twist threads give the best results when used from left to right, whereas Z twist ones do the opposite. Therefore, one should make one’s (buttonholes in buttonhole stitch that is) from right to left to achieve the best results.
I hope this clears up the confusion! Let me know if you would like a tutorial (video, illustrated, or both) on how to make buttonholes, of other thread-related topics.