Add custom field in product

Hello, guys, I was looking into you adding custom fields XMLRPC documentation and int there the customFieldType were these:

Contact, Company, Affiliate, ContactAction (used for Task/Appt/Note), Order, Subscription, or Opportunity

Now I want to add a custom field for product and I need the headerId. Can somebody guide me what should I do because currently I think there is no way of adding custom field in Product

Those seven you listed are the only tables available to place custom fields on. You cannot set custom fields on products.