A cattle gri or cattle guard, also known as a vehicle pass, or in New Zealand as a cattle stop, is a type of obstacle used to prevent hoofed animals, such as sheep or cows, from passing. It consists of a grid of bars or tubes, usually made of metal, firmly fixed on the ground with a depression underneath so that the gaps between them are wide enough for animals legs to fall through, but narrow enough that a vehicle's wheels will not. A cattle grid will allow wheeled vehicles to pass through the entrance, but will contain animals within the enclosure because they will refuse to step on the grid.