Balance Finger Vs. Balance Roller?

[noirrac1j]

Hello fellas,

Hey I want to ask does anyone know what is the difference between a balance staff with finger and balance staff with roller? I need to replace a balance (BFG 158 31/7), and I think its a roller because it has a jewel that is semicircular in shape on its striking face. Because I've worked on pin-levers, I know that some  balances have what looks like a finger on it--a little metal protuberance that strikes the guard pin on the lever itself. Do I have my facts right? Thank you very much for taking the time to answer!
Regards,

JC

Edited October 23, 2014 by noirrac1j

[bobm12]

Interesting, I would also like to know what is the difference and how to recognize them....if possible with a picture? Thanks in advance from me too!