Most JT handles have internal cooling channels that support internal cooling in the center of the spindle or (and) the end face of the spindle. The main structure is shown in the figure below. The BT handle is a Japanese standard, with a larger shoulder size than JT, resulting in an increase in knife weight. The 180 degree circumference has positioning, without positioning gaps that are detrimental to dynamic balance. Most BT handles do not have internal cooling channels, and some can provide BT handles with internal cooling channels. However, due to the thin neck of the pull pin of the BT handle (especially BT40 and below), increasing the central internal cooling channel may cause the pull pin to break and the handle to fall off. The main structure is shown in the figure below. There is not much difference in principle. However, in actual use, it is necessary to distinguish and not make mistakes.
BT machines cannot use JT tool handles, nor can JT machines use BT tool handles. Most standard configurations for European machine tools are JT type, such as DIN69871. Most JTs in Europe can choose to have central internal cooling or spindle end face internal cooling. Most standard machine tools in Japan, South Korea, and Taiwan are equipped with BT. The BT knife handle may not have internal cooling due to the thin neck of the pull pin. Because if internal cooling holes are added to the pull pin, the cross-sectional area may be too small and the strength may be insufficient.