For the sake of closing this thread: I have my PCIe x16 slots at ~80mm distance (center-to-center) and a 4-slot NvLink bridge (that I finally bought) plugged nicely in my cards. So in conclusion: 1 slot = 20mm . So if you have slots at 60mm distance, use a 3-slot NvLink bridge. For 80mm, use 4-slot.