The invention relates to the transmission of power and/or data from/to a stationary part of a machine tool (200) to/from an accessory (100) mounted in the spindle (210) of the machine tool (200). A first electrical link or interface la,lb,lc,ld provides electrical communication between the stationary part (200) and the spindle (210), and a second electrical link or interface (3) is provided electrically connected to the first electrical link at the accessory mounting area (230). The second link (3) is in the form of electrical contacts. The invention extends to an accessory shank (360) for mounting to the spindle (210) of the machine tool, and also to an accessory (100) e.g. in the form of a measurement probe, connected to the said shank (360).