Apartment type Description Single-Threaded Apartment[22] (STA), (ThreadingModel=Apartment) A single thread is dedicated to execute the methods of the object. In such an arrangement, method calls from threads outside of the apartment are marshalled and automatically queued by the system (via a standard Windows message queue). Thus, the COM run-time provides automatic synchronization to ensure that each method call of an object is always executed to completion before another is invoked.