hi im ordering a bong and im pretty new to them. Ive smoked them before but never owned one. Im getting the Mad Scientist V2 and it says that the joint size is 18.8mm > 14.5mm. What does that mean? Can i order a bowl that has a joint size of 14.5mm and an ashcatcher tree perc that is also a 14.5mm or do i need them to be 18.8mm. Thanks