I only use the yellow and blue glass head pins (I think by Clover) which are .4 thickness. It is much finer than .5 thickness, which is what you usually find being sold as "fine" pins. Around here .5 is the only thing available locally. I always buy a package of the .4 pins anytime I attend a quilt show and they are available from a vendor. I am terrified they'll quit making them and I won' t have any, so I have a couple packages squirreled away now. :D Because they are so thin, they cause little or no distortion in the fabric, and if you are careful (meaning I stitch one stitch at a time) you can sew over them. On the rare occasion when my needle has hit a pin, the pin just bends. They are so thin and flexible you can bend them even in pinning if you are aggressive about it. There are also some flower head pins which are .45 in thickness, and they are better than the regular .5 flower head pins. Those are easily identified because they are all light blue on one side and darker blue on the other side. Most all pins tell you the thickness on the package in small print somewhere.