Help on which air mixture screw i need?

im looking for a dellorto phva/phvb air/fuel mixture screw but under this section is like 3 screws anybody give me a hand i really need this to get to work an back?

 

http://www.dellorto.com/merchandise/products.asp?CategoryID=2&PartsectionID=26

 

cheers buddy got it ordered, will i need a spring and two washers, one being a plain washer and one being a 'o' ring? and if so could you tell me which order you put the washers/ 'o' ring? sorry about all the questions im just new to this stuff and want help before i modify