30mm box wrench on one end, 32mm on the other end. It's a headset wrench for bicycles, and those nuts can be in some tight configurations, so this wrench is a little thinner than most. Still thicker than a typical "cone wrench" though. Try not to put too much force on it or it might bend. Don't try to use it like a hammer or it will dent/crack. Treat it right, and use it only on bolts that don't need to be superman-tight, and it works fine.