An O-ring is a circular gasket made of elastomer, typically rubber, used to create seals between two parts. It's designed to be compressed in a groove, forming a tight seal against pressure or vacuum. O-rings are used in various applications, including static (stationary) and dynamic (moving) seals. 

Here's a more detailed description:

Key Characteristics:

• Shape: Round cross-section, resembling a torus or doughnut. 
• Material: Typically made of elastomers like rubber, but can also be made of PTFE or metal. 
• Function: Creates a seal by compressing against mating surfaces in a groove. 
• Applications: Used to seal pipes, tubes, pistons, cylinders, and various other interfaces in static and dynamic applications. 

How it works:

• The O-ring is installed in a groove between two parts. 
• When pressure is applied, the O-ring compresses, deforming to fill any gap and creating a tight seal. 
• The O-ring's elasticity allows it to return to its original shape after the pressure is removed, maintaining the seal. 

Materials and Considerations:

• Elastomers:

  O-rings are commonly made of elastomers like Nitrile Rubber (NBR), FKM (Viton), Silicone, and EPDM. 

• Temperature and Chemical Resistance:

  The choice of material depends on the specific application, considering factors like temperature range, chemical resistance, and other environmental factors. 

• Squeeze:

  The amount of compression or "squeeze" is crucial for proper sealing. Squeeze is the difference between the O-ring's outer diameter and the groove diameter.