You are buying 1 aluminum beam precision made of 6061 light weight aircraft grade aluminum. Made for high strength scaled moc-ups, physics experiments, or robotics, where an all plastic creation may not hold up.  Works with Technical gears, and have 9 holes at 8 mm spacing. All holes have 6 mm counter bores by 3/4 mm deep. Adding aluminum metal to a construction kit requires adult supervision, because its increase strength, leverage, and the ability to move heavy objects and do real world task. We custom CNC machine anything. Limited quantities available.