This is a strap that makes the headphones much more comfortable, just like on other high end headphones that use this style of suspension headband. 

I designed this suspension strap for the HD600 series (580, 58X, 600, 650, 6XX, 600, 660S2) as the other design that I tried was good but could be improved. Mine is wider for more even distribution of weight as well as having integrated clips from hybrid TPU + PLA as the tiny clips from the other design tended to break very easily. 

I printed the inset that replaced the original top pads from silk for nice metalic look. You glue the two tiny PLA block into the corresponding holes on the TPU strap to reinforce them. To assemble you remove the stock headband end stops and remove the cup from the headband. Then you insert the metal straps of the headphones into the holes of the TPU strap and insert the built-in in clips into the headband where the original headband stops were. 

As a side note, be careful moving the model around on the plate as it has negative and other modifiers