Purchased to replace OEM flare nuts on a 2012 Ford Focus. Fits perfectly. One-piece construction so we don't have to struggle to fit a socket, unlike OEMs where the chrome cover will degrade and result in sockets not fitting. It's 19mm, as OEM should be. If you can't fit the 19mm or get stuck in the tool every time, just buy the 19.5mm to remove the old factory ones and then put them in their place.