The internal temperature is an important index for the prevention and maintenance of a spindle. However. the temperature inside the spindle is undetectable directly because there is no space to embed a temperature sensor. and drilling holes will reduce its mechanical stiffness. https://www.roneverhart.com/Behringer-UL-1000G2-Wireless-In-Ear-Monitoring-System-US-584-to-608-MHz-p31393/