It looks like a foam insulator that would slip onto a steel line or cable. Perhaps for an anti-rattle?
It does not have a visible split in it, so the piece that it came off of may have been open-ended?
The 'screws' in it may be for locking it tightly in place?
Look for a 'clean shadow' on the tubing or rod(?) where it might have been? It may have been meant to stop a rattle against an adjacent tube or the floorpan?