I designed this arm to support a fan for my desk, it's modular and you can make it as you want. for each segment, you need 3 M5 nuts, a 15mm M5 washer , a piece of PVC pipe 20mm exterior diameter and 16mm interior and an M5 thread bar.
to connect the segments, you need 1 M3 20mm screw and 1 M3 self_locking nut.
the thread bar has to be 10mm longer than the PVC pipe
thread bar: http://s.click.aliexpress.com/e/DypKLxPK
M5 nut: http://s.click.aliexpress.com/e/45Gd9Nk8
M5 washer: http://s.click.aliexpress.com/e/qnHTvBvQ
M3 20mm screw: http://s.click.aliexpress.com/e/DNrzZwv2
M3 self locking nut: http://s.click.aliexpress.com/e/20ZXG1zI