14x1.5, #9 on here, sometimes you can get the fastener specs from these diagrams:
Shock Absorber Coil Spring
If I was getting these locally I would get the best ones I could get (at my local Fastenal they have a good selection of class 8 and class 10 metric hardware) in some form of lock nut. I would probably just get new Porsche ones since they are not too expensive. Pelican is the best for having these sorts of things in stock instead of having to wait 2-3 extra days and their shipping isn't too bad.
I keep meaning to start a list of small OEM Porsche parts that I need non-urgently but aren't worth a dedicated order, so that when I do make an order, I don't forget to add them
