With the development of external bearing designs, the standard shell diameter has become a considerable constraint, limiting both the diameter of the bottom bracket spindle and the size of the actual bearing balls in the races. Consequently, these external bearing designs can be less durable than older internal bearing designs. To address this problem several designers have promoted new standards for larger diameter bottom bracket shells, the best known of which is BB30 promoted by Cannondale. The name BB30 refers to the diameter of the spindle, not of the shell. Most of these larger diameter designs are using bearings that are pressed in. Since about 2015 there is now a T47 standard with a larger shell diameter and also threading. Some manufacturers (like Trek) are starting to implement this into their bicycles, while it is also possible to have threading cut into an existing 46mm pressfit and have T47 cups fit in there.