this is on the DOWNTUBE not the top tube.. made a mistake in the thread title
I've seen this on both an 1989 and a 1999 road bike.
1. what are they called
2. can they be removed/replaced? how about just the silver outer part? it seems like it's stuck on pretty good even though it's not fastened with a screw.. the small guide ends that are encased in plastic have rusted onto the silver parts so it would be easiest to just replace them if possible
3. can they be used to mount downtube shifters?