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 1a,1b,1c,1d 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.