The difference between 18- and 16-gauge sinks is the thickness of the stainless steel of which they are made. A 16-gauge sink is made of thicker steel than an 18-gauge sink.
The thickness of stainless steel is measured by gauge, with smaller numbers being a thicker steel and larger numbers being thinner steel. Stainless steel is steel that has been combined with other elements to increase its strength. Chromium and nickel are added to steel, and the higher the percentage of these elements, the stronger the steel is.
Sinks are usually made from 16- to 22-gauge steel. Sinks with higher gauge steel usually cost less money than lower gauge sinks. The thinner the steel from which the sink is made, the more susceptible it is to being accidentally dented during normal usage. Lower gauge sinks are better able to handle the vibrations that come with the use of a garbage disposal in the sink.
Higher gauge sinks typically produce more noise than lower gauge sinks when items are dropped into them. This noise can be reduced by the application of sound insulation to the underside of the sink. This insulation also helps reduce condensation on the bottom of the sink.