Rock sliders are an aftermarket accessory popular among four wheel drive vehicle owners who engage in more serious off-road driving.
Rock sliders are typically made of heavy-duty box section steel, although they can also be made from tubular steel as well.
They are welded or bolted (directly, L brackets and/or U brackets) on to the vehicle's frame, and their function is to protect the door sills and door bottoms from damage when crossing large obstacles (such as rocks - hence the name).
[1] Even though they serve relatively the same purpose, rock sliders come in four different types:[2]
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