<P> The hedgehog is not generally anchored to prevent movement, as it can be effective even if rolled by a large explosion; instead, its effectiveness lies in its dimensions, combined with the fact that a vehicle attempting to drive over it will likely become stuck (and possibly damaged) through rolling on top of the lower bar and lifting its treads (or wheels) off the ground . </P> <P> Industrially manufactured Czech hedgehogs were made of three pieces of metal angle (L 140 / 140 / 13 mm, length 1.8 metres (5 ft 11 in), weight 198 kilograms (437 lb); later versions: length 2.1 metres (6 ft 11 in), weight 240 kilograms (530 lb)) joined by gusset plates, rivets and bolts (or, later in the war, welded together) into a characteristic spatial three - armed cross with each bar at right angles to the other two . (This pattern forms the axes of an octahedron .) Two arms of the hedgehog were connected in the factory, while the third arm was connected on - site by M20 bolts . The arms were equipped with square "feet" to prevent sinking into the ground, as well as notches for attaching barbed wire . </P>

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