 Friction buffer stops are clamped 'loosely' to the rails, and when hit by a train that fails to stop correctly, move with the train for perhaps scraping the top of the rails, which absorbs considerable energy.In violent collisions, the buffers of adjacent carriages may become displaced relative to one another, allowing the carriages to telescope which is very dangerous.The risk of this can be reduced if the buffers (or fake buffers) have corrugations that grip each other and prevent the buffers becoming displaced and so leading to telescoping.