The radiator cap acts as more than just a "lid" for your radiator; it keeps your engine cool by sealing and pressurizing the coolant inside it. What makes the radiator cap special is that it is designed to hold the coolant in your radiator under a predetermined amount of pressure.
These are designed to raise the boiling temperature of water in radiator by pressure calibration. These have a vacuum valve to arrest damage to radiator. We are regularly exporting various types including equivalent to R123 and R124 with both stainless steel and brass fittings.