Always the Clover yellow and blue glass head pins which are 0.4 thick. They look just like the ones that are 0.5 thick, so be careful to buy the thinner ones. It really makes a difference. They don't distort the fabric and if you sew slowly you can sew right over them without worrying about harming your machine. They are so thin the needle will just nudge them out of the way. If you sew too fast and do hit a pin, the needle just bends the pin. I also have some flat plastic flower head pins I use when I need a longer pin (like pinning thicker areas, binding and such), which have all blue flower heads, dark blue on one side, light blue on the other side, and those are 0.45 thick.