Plastic on Bolts

I am working on the aileron bell cranks, the bolts sent by Van's have a plastic tube over the bolts, it is smaller than the grip length of the bolt. My first assumption is that these are to protect the threads but none of the other bolts in the kit have this and the tubing does not stayover the thread so it really does not portect things. Then I was thinking this must go into the brass bushing as well, but there is no indication of this in the plans. Has anyone else seen this, do I just throw them away?

Thanks

Thread Protection...

is all they're there for. Those longer bolts get to be relatively expensive, so a little extra protection for them doesn't go amiss.