Issue #24952: Clarify default argument of stack_size() in threading, thread

Patch from Mattip.
diff --git a/Doc/library/thread.rst b/Doc/library/thread.rst
index 8a625f8..f1cee24 100644
--- a/Doc/library/thread.rst
+++ b/Doc/library/thread.rst
@@ -98,7 +98,8 @@
    Return the thread stack size used when creating new threads.  The optional
    *size* argument specifies the stack size to be used for subsequently created
    threads, and must be 0 (use platform or configured default) or a positive
-   integer value of at least 32,768 (32kB). If changing the thread stack size is
+   integer value of at least 32,768 (32kB). If *size* is not specified,
+   0 is used. If changing the thread stack size is
    unsupported, the :exc:`error` exception is raised.  If the specified stack size is
    invalid, a :exc:`ValueError` is raised and the stack size is unmodified.  32kB
    is currently the minimum supported stack size value to guarantee sufficient
diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst
index 04a6ebe..ccb922b 100644
--- a/Doc/library/threading.rst
+++ b/Doc/library/threading.rst
@@ -194,7 +194,8 @@
    Return the thread stack size used when creating new threads.  The optional
    *size* argument specifies the stack size to be used for subsequently created
    threads, and must be 0 (use platform or configured default) or a positive
-   integer value of at least 32,768 (32kB). If changing the thread stack size is
+   integer value of at least 32,768 (32 KiB). If *size* is not specified,
+   0 is used.  If changing the thread stack size is
    unsupported, a :exc:`ThreadError` is raised.  If the specified stack size is
    invalid, a :exc:`ValueError` is raised and the stack size is unmodified.  32kB
    is currently the minimum supported stack size value to guarantee sufficient
diff --git a/Misc/ACKS b/Misc/ACKS
index d732bf0..ba3e3fe 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -875,6 +875,7 @@
 Simon Mathieu
 Laura Matson
 Graham Matthews
+mattip
 Martin Matusiak
 Dieter Maurer
 Daniel May
diff --git a/Misc/NEWS b/Misc/NEWS
index ebf2ed5c..1cc3f15 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -163,6 +163,9 @@
 Documentation
 -------------
 
+- Issue #24952: Clarify the default size argument of stack_size() in
+  the "threading" and "thread" modules. Patch from Mattip.
+
 - Issue #20769: Improve reload() docs. Patch by Dorian Pula.
 
 - Issue #23589: Remove duplicate sentence from the FAQ.  Patch by Yongzhi Pan.