The lamp above has an inner tube outside diameter of 1-1/8 inches.
Please note where the arms of the caliper are touching
Lamp wicks are always measured in inches as most of them were made pre decimalisation
The Radiant heater below shows a wick diameter of 75 mm, mm because these heaters were made post decimalisation
Please note where the caliper arms are touching avoiding the stepped edge
© Parafinalia