Two vibrating transmitters as used by the British Army.

At the left: manufactured by Siemens Bros. Model Mk V, year 1919, No. 5945.

At the right: manufactured by ATM Co. Ltd. Model V, year 1915,  No. 2488.

Both contain at the front “Tommy” bars to adjust screws and on the left side two brass screws to mount the unit on a wooden table. The knob can be screwed on the manufacturer´s plate, for transportation purposes.