I have a question: there seems to be a screw missing. It's underneath the top tube, similar to the allen-head screws that are in the frame for water bottle cages. There is only one hole though. It's underneath the top tube towards the front. Any ideas what this could be used for? The threaded hole is smaller than the water bottle cage holes, i.e. the allen-head screws for the water bottle cages do not fit in this hole.