The term "primary link" is correct and can be used in written English.
It is often used to refer to the main connection between two entities or concepts. For example, you could say: "There is a strong primary link between market research and successful product engineering."
Li, Y. I. et al. RNA splicing is a primary link between genetic variation and disease.
After that, he said, the Mashco had regarded him as their primary link to the outside world.
Well done Yang, whose paper RNA splicing is a primary link between genetic variation and disease is out today [Link].
As officials trace Mr. Atta's movements through the United States and Europe, investigators have tentatively concluded that he was the primary link among the 19 hijackers.
Two flights a week from Nadi, Fiji, constitute the primary link between Kiribati's capital and most-populated atoll, South Tarawa, and the distant outside world.
The official said Mr. Somali was the primary link between Qaeda leaders in Pakistan and the network's allies in East Africa, including the Somali militant group Al Shabaab.
They will have substantial responsibilities for patient care and usually serve as the primary link between the clinical services and the Transfusion Service/Blood Center.
Just as Heathrow to New York JFK is the 21st century's leading intercontinental air route, Southampton to Manhattan was the primary link between Europe and the US.
Mr. Gaffney would emerge as Mr. Yerushalmi's primary link to a network of former and current government officials, security analysts and grass-roots political organizations.
Community Affairs, which is the state's primary link to municipalities, would also take over the Office of State Planning, now a part of the state Treasury Department, to help local governments achieve statewide land use goals, Ms. O'Connor said.
While the evidence continues to point to the Pakistani Taliban as the primary link, a senior official said Mr. Shahzad "appears to be at the intersection of a whole lot of strands".
