16 PCI Express lanes is the default connection width for graphics on most motherboards.
On many dual graphics systems, two x16 PCI Express slots are powered by two slots running in x8 link mode.
This is the PCI Express connector of a graphics card with connectors taped to run at x8 PCI Express.
We had to tape many of the PCI Express contacts to force the test system into x4 PCI Express mode.
Here is an image of the same card, but with more connectors taped. This one will run x4 PCI Express.