If i was using these pully's what width of belt should I use...? I don't know which number means what?

Pullys

http://uk.rs-online.com/web/p/products/ ... 4E4F4E4526

http://uk.rs-online.com/web/p/timing-be ... s/0745719/

belts

http://uk.rs-online.com/web/c/mechanica ... 4294958223