JER 52:21

21 Forsooth of the pillars, eighteen cubits of height were in one pillar, and a rope of twelve cubits compassed it; certainly the thickness thereof was of four fingers, and was hollow within. (And concerning the pillars, each pillar was eighteen cubits in height, and a rope, twelve cubits long, was needed to go all around it; its metal was four fingers thick, and it was hollow within.)