I had my driver's side door check start to fail. It didn't lock solid, but it was making horrible noise / pops, with dicey resistance and the worse part - the door jam was flexing where the door check connects the door to the car's door frame (see pics - it will make sense).
So here is the problem with the inner door frame. The door check (strap?) connects via a pin and reciever. That pin / receiver piece is a plate that spot welded in place (from the inside?). As the door check wears out (I think what happens is that the grease inside the door check deteriorates) the plate starts getting stressed. Cracks start to appear on the paint, and then the spot welds start to fail. I had one fail (top left corner). In the first pic, you can barely see where the other spot welds are (two per side of the pin receiver).
Since I was going to do the door check, I wanted to repair the pin / receiver / plate as well. I had a slight hole where the spot weld had broken (sorry - din't get a pic before I drilled the hole). I went to the hardware store and brought home a variety of bolts.
I decided to go with a 5mm .80 x 12 bolt. I wanted it to be beefy enough, yet I didn't know how wide the plate was inside the door. I couldn't go crazy big with the bolt as I risked drilling into the edge of the plate rather than drilling into the plate safely inside the edge.
You can't put a nut behind the plate - no way to get to it, even if you remove the hood release handle and try to go up through the kick panel. So, I needed to put threads on the plate to draw it tight against the door jam with the bolt.
Per my tap and die set - I drilled a #19 drill (.166 decimal equivilant) so I could tap it with a 5mm x.80 tap. Some folks have used a sheet metal screw. I wanted the repair to be a little more elegant.
I just put it on and it seemed to work nicely. The bolt pulled the plate up gainst the door jam sheet metal. The door jam is not flexing and the new door check is like butter
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In the pics you can see that the plate behind the door jam sheet metal (pic #3).