O-rings are one of the simplest, yet most engineered, precise and useful seal designs ever developed. They are available in various metric and inch standard sizes. Sizes are specified by the inside diameter and the cross section diameter (thickness).
Hose barbs are cylindrical pieces or parts for attaching and securing of hoses (tubing). The barb-like rings on the cylindrical piece allow for an easy push-connection of flexible plastic or rubber tubing that is not so easily disconnected.