Download the 20D331K datasheet PDF.
This datasheet also includes the 20D180L variant, as both parts are published together in a single manufacturer document.
METAL OXIDE VARISTORS
Transient voltage surge suppressors 20D series Model Number Maximum Allowable
Voltage Standard High AC DC Surge (V) (V) 20D180L J 11 14 Varistor Voltage
V 1mA (V)
18(15-21).