I'm trying to purchase front lower control arms for my 2007 C 70. It states for Vin #2743, and 15mm stud. What does the Vin requirement mean? I've also seen bigger studs. What should I purchase

 

Here's the parts page. Before chassis # 2026 (the last four digits of your VIN) takes a 31277464 and after 2027 uses a 31277463 for the left side of cars without level control. Early cars have 18mm something, later have 21mm something (wrench size on the ball joint nut? and the ball joint shaft size will be different also along with #5 the steering knuckle)