The Gigabyte Z170MX-Gaming 5 comes with three PCI Express 3.0 x16 slots and one PCI Express 3.0 x1 slot. There is also an M.2 slot supporting both PCI Express 3.0 x4 and SATA-600.
The two first PCI Express x16 slots work on x16/x0 and x8/x8 configurations, which means the first slot work at x16 if the second one is unused, but it it is occupied, they will both work at x8. The third PCI Express 3.0 x16 slot works always at x4 speed.
The motherboard supports CrossFire with up to three video cards and SLI with two video cards.
The PCI Express x16 slots are covered by stainless steel shields that work as a shield against interference, while also improving mechanical strength of each slot.
Figure 2: slots