Hi,
This was a 7.65mm para or .30 luger version and still is.
I believe the Mauser Parabellum can be used with the same spring. Some German companies sell loose 7.65 and 9mm barrel/receiver combo's so that people may fire both calibers with the same pistol.
Personally I'd expect a slightly stronger spring in a 9mm outfit. But the Wolff replacement spring I got a while ago, also mentioned both 7.65 and 9mm support.... I guess it's not an exact science