Buttons if sewn directly onto the fabric will lie completely flat against the fabric, there is little space between the button and the garment to allow an additional layer of fabric to sit between when the button is fastened and passed through the buttonhole. This is why a thread shank is required. It lifts the button slightly above the garment it is sewn to, allowing the other side of the garment with the buttonhole to sit neatly underneath the button once it has been buttoned.
When sewing on a button, use approximately 1 metre of thread. Double up the thread and pass the looped end through the eye of the needle. Make all the ends level and then tie a knot. This means that you will be sewing with four strands of thread, making each stitch stronger- so you will need fewer of them!
Make sure you have a good knot so that it will not pull through the fabric, or sew a few locking stitches into the fabric first.
Pass the needle from the back to the front of the garment and through the first hole of the button.Slide a matchstick/ cocktail stick/ thick end of a machine needle under the button, then thread the needle back down through the other hole of the button.
After several stitches have been made through the button, pass the needle so that it comes through the fabric under the button and remove the matchstick. Wind the thread around the button shank three or four times in order to strengthen the button shank.
Pass the needle through to the underside and sew a few locking stitches through the visible threads.