What is the lens coefficient value of B cups? (k1, k2)

I made a VR viewer from the spare eye cups of my DK2.

Because the lens are much better then the default cardboard ones the distortion is off.

I can set distortion manually using this:
https://www.google.com/get/cardboard/vi ... generator/

But I need to define physical properties of the B-cup lens. I tried googling this and it's not described anywhere.

What should be the k1 and k2 value for B cups?