Build your own expansion tank, modify a radiator or solve a myriad of other cooling system problems with our weld-in radiator cap neck. It comes to you fully machined with our unique pressure ramp and precision sealing surfaces. It is designed to weld into a tube or hole that is 1.125" diameter. A step in the body also allows it to fit intoa tube or hole that is 1.25" diameter. For a low profile version see part #WN0012W.