To do the straps I had no plan - I just vamped.
I had three springs with 8 mm diameter each so I took a brass tube of 4 mm diameter cutted two pieces of 18 mm down and made M3 threads at each end. I got to my sewing place where I had some chicago screws (screws with a thin but very wide head) and two ball screwnuts wich were good for combining a two-piece strap.
To prevent that the springs bite my hair I wanted to wrap the leather a little bit around and with this measure I did a bit of leather withe the slippery side inwards. The springs were colored with a bath in linseed oil and fire and I´m still not sure to use 3 or 2 springs at each side, thats why there are 3 springs but only 2 assembled..
The leather inside the cups were made by cutting carefully more and more and sewed by hand. I pressed them in weat and dried them with a small flat-iron. They are holded by the screws as you see.