william bailey's 1955 chevy 210

This is the third set of ladder bars I've done and I picked this set up off EBAY. They seem to be good and heavy and well built. I just can't figure why the end of the bar that fastens to the the crossmember has an oblong slot. The other bars had an oblong slot too, BUT the threaded end ran all the way into the slot and you screwed an end into that and your bolt ran through that end. These bars don't have such a setup and I'm wondering what kind of bushing goes into the slot for attachement to the crossmember. Any ideas? If this picture doesen't upload on the post, there is a picture of the bar end on my website.

thanks

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