plugs in rear spring mounts?

[06boblee]

When I took my rear springs off, there were cork "plugs" on the inside of the threaded hole in the frame mount where the spring bolt goes. They appear to have been put in the hole and then the bolt pushed it in until it was tight. I am assuming this was done to keep stuff from getting to the threads. Was this a factory deal, or someones past great idea?

[ashyers]

Mine had the plugs too. I made new ones with some wine corks . Also used loctite one the bolts to keep crud out.