Screwing in a PCIe card

[dimme]

I have a early 2008 mac pro a while back I added a NewerTech eSATA Extender Cable to the internal sata. the sockets connect on the back like a PCIe card. With the standard apple bar that supposed hold everything in place the endplate will not stay in place. I have a large collection of screws fron building many PC but nothing will tighten down in the screw hole. They seem to start but only o in a few turns. Has anyone faced this problem? I not sure what to try next.
Thanks

 

[DanielCoffey]

You could try putting a piece of card between the folded over end of the blanking plate and the apple fixing bar - it sounds as if the material of the blanking plate is a little thin maybe?