Herman Miller Aeron Chair as seen here http://www.hermanmiller.co.uk/products/seating/performance-work-chairs/aeron-chairs.html doesn't have a headrest so i knocked one up - not pretty but does the job and is very comfortable.

Is fits together in an obvious way. Need lengths of m8 smooth rod, m8 coach bolt, m4 cap heads, m4 wing nuts, and m4 nut. Looking at the model files should indicate lengths. Most importantly some flexible PLA for the weave. You need to print the MAIN CLAMP and JAW 100% infill the JAW seems to be stronger in PLA but the rest should be in ABS at 50% infill.

The jaw will need some filing down as PLA has a different expansion (for me anyway). The model files have a good gap for the jaw into the clamp but printing shrinks in different ways when using multi types of plastic.