Gladhands and gladhand seals are used when connecting pressurized air hoses or brake lines from trucks or semi-tractors to trailers. These gladhand connectors or gladhand couplings form an interlock between truck and trailer. Gladhand seals prevent air from escaping once connected. Gladhands and gladhand seals are typically designated by color: red for emergency brake lines, blue for service air lines, and black/silver for universal use.