Some steel and iron fence manufacturers will cut corners here.  Especially in the rail-to-picket connection (the rail is the horizontal piece and the picket is the upright one).  The worst ones we’ve seen is companies using rivets or screws to connect the pickets to the rails.  While this works fine on a lighter aluminum fence, it does not work as well on an iron or steel fence.  Not only does a weaker connection result in a ‘loose’ feeling panel, but the rivets can allow movement which can scratch down to bare metal and create rust spots.