13/18 mm o-ring (heater element)

This special heat-resistant o-ring fits over the terminal on standard hot tub heater elements, and seals the junction between the element and the inside surface of the heater tube.

It is also associated with the Balboa Niagara pumps' drain plugs.

Dimensions
Inside diameter: 13 mm
Outside diameter: 18 mm
Thickness: 2.5 mm