The best pins for piecing are very fine pins, because they cause minimal or no distortion. I like pins made by Clover which are .4 thick and have clear blue and yellow (in the same pkg) glass heads. Clover also makes identical pins in the .5 thickness, which is thicker, and the size commonly called "thin" by most manufacturers. Don't buy .5---buy .4 thickness. I have to buy them at quilt shows because they aren't sold locally. The closest I can get locally are flower head pins which are light blue on one side and dark blue on the other side and are .45 thick. I'll use those in a pinch, but prefer the thinner .4 thick pins. They are so fine I sew right over them---slowly---and have never broken either a pin or a needle. If you sew slowly, the needle seldom hits a pin, and if it does, it usually will just push the pin a bit. On the rare occasion that the needle does hit a pin, the pin is so fine that it just gets bent. These pins are so thin I have to remember to be gentle in placing them or they will bend slightly. They're the best!