Spark Plug
WARNING: This page is about a different car, the 2002 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
The spark plug's thread diameter is 14 mm (0.551 in) and the gap is controlled to a value between 1.0 and 1.1 mm (0.039 and 0.043 in).
Courtesy of SUBARU OF AMERICA, INC.