Here's a scarcely seen glass radio strain embossed with the British Air Ministry's circa WW2 embossing: A {crown] M (one eyelet) [id=187660858] and 10A-7652 (bottom eyelet, same side) [id=187660961]. I believe these were previously "classified" insulators made during the allied war effort by Phoenix Glass (how they referred to themselves) but their official name was the British Heat Resisting Company, Ltd. This beautiful blue aqua strain measures 7 1/4 inches long from end to end and hanging from an eyelet measures 6.5 inches long.