Sealing O-ring

An O-ring is a mechanical gasket in the shape of a torus (doughnut-shaped ring) designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface. In lens mounts and housings, it specifically prevents the ingress of dust, moisture, or other contaminants while maintaining internal pressure or vacuum conditions critical for optical performance.

The O-ring creates a seal through elastic deformation when compressed within a gland (groove). The resulting contact pressure between the O-ring and mating surfaces blocks the passage of fluids or gases. Its circular cross-section allows it to seal in both axial and radial directions, accommodating minor movements and thermal expansion.