Abbr. for "Black Iron Pipe." Also referred to as "Inch and a half schedule forty I. D." Most commonly industrially used for gas lines, but used in the theatre for lighting positions. Legend has it that in the late 1800s, when theatres converted from using gas lighting to electric lighting, the pipes were removed and re-used as fly system battens. May not necessarily be colored black unless painted. Most common size in theatre is 1.5" which has an exterior diameter of 1.90." Usually steel, not iron, and comes in two common strengths: Schedule 40 for general use, and Schedule 80 for heavy-duty. Exact specifications here. Is somewhat being replaced by 50mm (2" OD) aluminum thick-wall tubing OR 1.5" Schedule 40 aluminum pipe, but aluminum is not as strong as steel and cannot be threaded. Other useful abbreviations: TOE = Threaded One End TBE = Threaded Both Ends Tip: Wrap a couple of wraps of gaffers tape around the threaded ends to protect them when not in use. Always use the courtesy tab with gaff tape.