These are values for parameters that control the run time behavior of the thread in terms of its competition for resources and what happens when it exits.
Larger values imply greater importance.
A detached thread cannot be join ed by another thread and disappears when it exits. The Evaluator Manager ignores its return value. This allows the user to set the space allocated for a thread's stack used for the evaluation of the C function calls in this thread. If strange warning messages appear from the internal thread utilities, you can try changing increasing this value. Of course, the large this value, the fewer the number of threads as there is a fixed size for the resources shared by all the threads in a process.