According to Compendium 7 of “Wireless for the Warrier” by Louis Meulstee & Chris Bisaillion, this is a WW2 Morse Key & Plug Assembly 9A v4.1 WT 8 Amp No.2 Mk III. The straps enable it to be Leg Mounted. The case has the Army Stores Code ZA17693.
It would have been used in conjunction with a No. 76 Wireless set, (a portable lightweight CW transmitter, 2-12 MHz, with a range of over 300 miles, introduced in 1943), and the R109 receiver.
In great condition with a few surface scuffs. A wonderful find for all collectors of military keys or radio communication aficionados!
Summary Black Bakelite & Metal Marked ZA17693 (Army Store Number) on the side KEY W.T. 8 amp No.2 MK.III Leg Mounted Large No.10 plug
Approximate measurements: Base Width: 5.1cm (2″) Base Length:- 14.5cm
