O-rings are one of the most common seals because they are inexpensive, easy to make, reliable, and have simple mounting requirements. They create air tight/ water tight seals.

The seal is designed to have a point contact between the O-ring and sealing faces. This allows a high local stress, able to contain high pressure, without exceeding the yield stress of the O-ring body. The flexible nature of O-ring materials accommodates imperfections in the mounting parts. But it is still important to maintain good surface finish of those mating parts, especially at low temperatures.

Each individual o-ring weighs 1 grams and is shipped in packets of 6 pieces.

The TAT7 case comes with two (2) pieces of pre-installed o-ring. 

Whilst the o-rings are not easily damaged, repeated opening and closing of the TAT7 case may wear out the o-rings.