The phrase "main means" is correct and can be used in written English.
For example, you can use the phrase "main means" in a sentence like this: "Writing is the main means of communication in the modern world."
Tour de main means skill or knack.
Pictures have become one of the main means of communication.
Railways are the main means of transport in Lithuania.
For many of these people, walking is the main means of transportation.
The land, then the main means of production, belonged to the tribe.
Buses, trucks, and minibuses are the main means of transport for the population.
Privately owned bus services are the main means of public transportation inside the urban agglomeration.
The main means of birth control is still abortion, as it was in the Soviet era.
The main means of limiting it is to create protected areas such as national parks.
She is sure that the terrorists will some day bomb the subway, her main means of getting to school.
Its buildings have been blasted by artillery fire, one of the Russian military's main means for dealing with rebel snipers.
