Reading the Two Digits
The first digit rates dust resistance (6 being fully dust-tight); the second rates water resistance — IP65 withstands low-pressure water jets, IP66 withstands stronger jets, and IP67 withstands temporary full immersion up to 1 meter.
Matching the Rating to the Use Case
An outdoor security camera facing direct rain exposure needs at minimum IP66; a GPS tracker mounted in a vehicle wheel well benefits from IP67’s immersion resistance — over-speccing adds cost, under-speccing risks field failures.