Pro II's are the standard look hub that uses 6 bolt rotors and normal spokes. The Pro III's are available in several versions (AM, XC etc) and are only available when built as part of Hope's wheelset range as they use straight (non elbowed) spokes. They use custom 3 or 4 bolt discs dependant on version and these are included with the wheelset when you purchase it. They also come fitted with stainless steel bearings as standard.