Stainless-steel housings and front faces on proximity sensors withstand physical and environmental abuse. And the thicker the steel, the more abuse the sensor can withstand. But RF frequencies must penetrate the face for the device to work, so it cannot be too thick. Still, sensors typically have rated sensing distances of 2, 5, and 10 mm (depending on barrel diameter). And because steel sensors are monolithic, there is no way for dust, moisture or other elements to get inside. This makes them well suited to wet, damp, and wash-down environments.