Spark key manufactured by Telefunken (a joint venture of Siemens and AEG both of Germany) C. 1910.

One of the labels at the base reads “Type C.T.K. Appt. No. 1661”.

The spring, the guard ribbon, the trunnion fixing screw and the screw and nut adjusting the gap are not original, but were made  by myself following the manufacturer´s design.