I also highly recommend you use .4mm thick pins when piecing. I use the blue and yellow glass head pins from Clover. Most "fine' or "super thin" pins are .5 mm thick---a big difference. Watch what you buy because Clover also makes the exact same blue and yellow glass head pins in the .5 mm thickness. Those I find at JoAnn's but that's not what you want. The .4 mm thick pins are so fine they cause almost no distortion in the fabric and you can actually sew over them (slowly). They are so thin the machine needle usually just nudges the pin aside if it hits. Occasionally I will hit a pin dead-on, in which case the pin is ruined, but no harm comes to the sewing machine or it's needle. These pins can't be used with silky fabrics because they will fall out!