Graphics card maker Colorful, which recently designed the GeForce GTX 460 and GTS 450 iGame series of graphics cards, found out that its exorbitant cooler design (for mid-range graphics cards) may cause problems for users wanting to install two of these cards in SLI, because a large heatsink obstructs most rigid types of SLI bridges. Unlike with ATI/AMD, NVIDIA leaves it to the motherboard vendors to supply bridge cables.
Source: Techpowerup