Y'all,

While doing the thorough cleaning of my 300td's interior, I removed the seats and noticed a hole in the carpet on the sill, a bit forward of where the lower end of the seat belt attaches. There's a captive nut underneath, in maybe a 10x1.25mm thread size. Thus, it's too small to make it an alternate location for the seat belt attachment point. I made a point to look for this "feature" in the W123s in the junkyard the last time I was there, and they all had this hole with the captive nut underneath. What is this for?

Thanks,
Shawn