The Mastercool 43708 Radiator Cooling Test Cap Adapter with Vent is designed for use with the model 43707 and 4310 Combustion Gas Leak Testers. The adapter provides a leak-free secure connection to ensure the correct testing of a cooling system without the use of a rubber cone. The adapter can be used with caps from Mastercool Radiator Test Kits (43300, 43301, 43302, 43305 and 43306 - sold separately).