the black spring?

exactly what is it and where does it go?
i want to put one in my v, but i dont know nothin about them, can sombody fill me in

(where to puchase, how to put in.......)
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V-force (stock)

 

The black spring mod is for the p650 and I dont know anyone who has put in the Vforce. So far there doesnt seem to be a need to change out the driven spring on the V

You can read more about it here