As mentioned before your wheels are OEM 17” Boxster twists.
The 18” Turbo wheels (also twist style) were available in both solid and hollow spoke, and fist appeared on the 993 then the 996 & 986.
I have the 18” 5 spoke Carrera lightweight wheels on my ’97 Boxster and have not run any problems driving on the street. My mention of the issue was just to give you a heads up.