Button loops go along the closing overlap edge of a garment and they extend out from the edge. … This is the length of the button loop. Loops can be made individually, or they can be made from a continuous length, but this measurement is key to consistency.
To sew one button loop with a 15mm (5/8in) seam allowance, make a strip 4.5cm (1¾in) wide by at least 10cm (4in) long. Cut it longer if you want to make more than one loop – in fact, it’s easier to sew a longer piece without it getting sucked under the needle plate, and cut it to length later.
Appearance. Designed with a hollow protrusion structure in the rear, shank buttons are also referred to as buttons with hidden holes. These buttons are sewn onto the garments through the hollow protrusion using the sewing threads. Flat buttons are also referred to as buttons with visible holes.