Wikipedia contributors, ".th," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=.th&oldid=221350238
It is administered by T.H.NIC Co., Ltd. (THNIC), the corporate entity of Thai Network Information Center Foundation.
Registration of a .co.th domain name is a complicated procedure, for this reason most Thai websites prefer to use a .com name. In order to register a .co.th domain name the registrar in Thailand requires copies of company documents in the same name as the required domain name, so for example if an entity required acme.co.th the entity would need to have a registered company called Acme Co., Ltd.
A company can only register a single .co.th domain with the company name or initial name of company, and/or one .co.th domain name per trademark.
In 2018, the foundation advance to the registration for authentic using of persons (natural persons and juristic persons); therefore, the foundation reserves the right to consider and decide the number of domain names of each person on a case-by-case basis. The person who registered more than one domain name from all categories must comply with the following conditions:
THNIC admits .th registration only third-level domain under seven groups of predefined second-level domains:
Second top domain
In 2010 a new top domain was registered and introduced for Thailand, intended for domain names in the local language. This top domain is .ไทย. As of 2011, thousands of sites with this domain are active.
It appears that the Thai second-level .ไทย domains are assigned directly to sites with English .in.th domain names. Another groups of .th domains must use third-level .ไทย domains, as in the table above.