Any ideas why this random spacer on the base of a bridgeport where head nods?

Starting to work a little on the base and there is this spacer someone had put under this bolt head. It obviously doesn't go there, but people generally don't put random hardware on machinery for no reason. It doesn't even fit the bolt diameter (spacer has much larger i.d.) It's under the head of the bolt on the right. Any ideas what it's purpose could be?





Here is a pic of the spacer by itself.



I've pulled the bolt out and the bolt is not too long for the threads, so it's not there to take up space. Also the threads on the bolt look nice and it turns in all the way nicely, without the spacer.

The Bridgeport parts manual has some sleeve they show (looks like for the bolt hole in question) but I don't see how that would fit on this machine. See page 4-19, part #37 of this link http://www.hardingeus.com/usr/pdf/Kn...sIPartList.pdf

Here is the bolt and spacer removed.

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