Braking equipment for railways and subways. Railway Air Brake Hose Coupling Connector R23
The main consumers of R23 hoses are enterprises producing and repairing locomotives and wagons of all types of rolling stock for railways and subways.
The R23 connector hose is designed to connect the air brake mains of adjacent units of rolling stock and supply air to the brake main under pressure up to 1 MPa (10 kg/cm2).

https://www.railway.supply/en/railway-air-brake-hose-coupling-connector-r23/