'primary product' is correct and commonly used in written English.
For example, "This company's primary product is a line of organic soaps."
In this rural sector, production of the primary product (plantation crops, timber, beef, mineral, etc).
Hardwood boards are the primary product of the state's sawmills.
Primary product (see Table 1 to this part).
A downward influence is thus exercised on primary product prices.
The problem is the obvious shortcomings of the primary product, Donald J. Trump.
What the U.N. offers its members — its primary product, as it were — is legitimacy.
By contrast, the primary product in broadcasting was information, broadly defined.
Its primary product is the Focus, one of the best-selling cars in the world.
Following excitation of the trans chromophore, a ground-state primary product is formed within picoseconds.
Central States Indemnity's primary product line is credit-card credit insurance distributed through card issuers nationwide.
A chemical manufacturing process unit is identified by its primary product.
