Fill 20% on the layers.
Blending Options-Gradient Overlay



Gradient’s parameters:



Make a copy of the new made layer and choose the Free Transform option to minimize it uniformly. Fill 30% on the layers.



Pick up again the Ellipse Tool (U) to represent a kind of clamp.



Fill 0% on the layers.
Blending Options-Gradient Overlay



Gradient’s parameters:



Make five copies of the new made layer and place the copies the way it is demonstrated on the next image.



The final result!

View full size here.