Radiator Key
It seems inconceivable that in the 21st Century a UK manufacture is still producing Radiator Keys.
Monument Tools manufacturers a number of radiator keys for different applications
2058J Radiator Key for Bleed and Balancing
2059M 4 Way Radiator Key
2053U 3in1 Radiator Key
2054X 4in1 Radiator Key
2051O Twinpack of 2053U/ 2054X Radiator Key