@Laurie *******
- under the METV on arrival you will be issued a Permit to stay 60 days.
You can apply once in Thailand for this to be extended by 30 days for a fee, after which you must leave. You may then re-enter and get another Permit to stay 60 days.
The 6 months refers to the time period (window) the METV is valid from/to, and not the period of time you may stay - this is determined by the Immigration Officer and Permit issued.