An O-ring is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a disc-shaped cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface..
#10-24 x 3 in Combination Phillips/Slotted Round Machine Screw, Zinc Plated Steel, 100 PK Commonly used with flat or lockwashers. Especially useful in metal-to-metal or where heavy duty fastening is required.