All immersion heater spanner size measurements are A/F (across flats) which measures the distance between two parallel edges of the octagon that has been cut into the head.
Metric measurements are given first in millimetres. Imperial measures, in inches, are given afterwards in brackets.
Standard immersion heater spanner sizes
The majority of immersion heater spanners are made to fit the standard size of immersion heater element and measure 86mm (3 3/8″) A/F.
