Skew lines

This picture shows two skew lines. They exist on the planes of two steel girders. These are used for supporting buildings and are usually welded together. I found it on the internet at:
http://www.google.com/imgres?q=steel+girder&um=1&hl=en&client=safari&sa=N&rls=en&biw=1280&bih=738&tbm=isch&tbnid=M3IYIgHRL68ELM:&imgrefurl=http://www.heimer.com/Photographs/structure.html&docid=At-7jZ27sPCVGM&imgurl=http://www.heimer.com/images/photographs/structure/main_steel_girder_1.jpg&w=480&h=322&ei=1qWAULzADqbu0gGNnYGgAQ&zoom=1&iact=hc&vpx=856&vpy=108&dur=609&hovh=184&hovw=274&tx=179&ty=116&sig=109637316179286308971&page=1&tbnh=139&tbnw=222&start=0&ndsp=21&ved=1t:429,r:3,s:0,i:146