To the right are some scarlet runner beans on a normal, wooden stake and twine trellis. I planted bean and cucumber seeds the recommended 3 or 4 inches apart, and this is a good example of how full they will grow when doing well. Next year I may finally learn and keep the plants 6" or more apart. It is possible to over-plant beans and jeopardize the yield by overcrowding.
These purple podded pole beans are growing against a fence at a school garden. This type of wrought iron fence is a bit too slippery and wide for beans to latch on to, so it's necessary to add some type of trellis netting or twine, as I have done. With such assistance, the beans will engulf the fence.
Below are some more pole beans that are trellising on chain-linked fences, which seem to do just fine.