How to create a new fieldtype that sets it's DB column to int

I mentioned this on Slack the other day but no one has responded, so I’ll try here.

I’m making a new add-on and it saves only an integer value in the CP, and when the field is created, it sets the DB column to text, not int. How can I set the column to int? I tried this but it does not work.

public function save_settings($settings)
    {
        return [
            'field_content_type' => 'integer', // I tried 'int' too
            'field_fmt' => 'none',
            'field_show_fmt' => 'n',
            'field_wide' => true,
        ];
    }