O-ring is a ring that has a cross-section that looks like "O". X-ring is a ring that has a cross-section that looks like "X". See https://en.wikipedia.org/wiki/

O-ring is a ring that has a cross-section that looks like "O". X-ring is a ring that has a cross-section that looks like "X". See https://en.wikipedia.org/wiki/O-ring#Other_seals https://en.wikipedia.org/wiki/O-ring#Other_seals