This isn’t much of a secret, but I’m sure it will come as a surprise to some 9-5 owners. The oil drain plug on the SAAB 9-5 is 1/2 inch and not 13mm. The 13mm socket will work, but I think you’d run the risk of damaging the plug and the job is easier with the correct half inch socket.
Here is a photo of my drain plug. Notice the big drip of oil, how embarrassing. I had better tighten that before I lose too much oil and leave a mess on the garage floor.
And here is a blurry photo of my half inch socket securely placed on that plug. A little pressure with the socket wrench and the drip is gone. And I swear the photo didn’t look blurry on the camera screen. I’ll retake the photo soon.
I wonder what other standard/English sized parts there are on the 9-5. The 5/8 inch spark plug is the only other thing I’ve come across that wasn’t metric.