There is but you have to have both the gear and the materia on your person. So for instance you have a str III materia which is +4 anda cobalt belt nq. You cna go to the meld screen on any class and select both the belt and the materia and you will see the success rate as well as the stat amount that will be given. So cobalt belt has 5 str already on it the materia stat increase will show in red (which means not total bonus is given) adding only +1 str so the stat cap for str on a cobalt belt is 6str. Normally on similar stats like vit and dex the stat cap will be the same but parry stat cap is +10. Now if these is true of all belts at that level I do not know. But at least for cobalt i know and I do not have to waste te str III.