No, it’s a barrel adjuster for either in the frame, the rear derailer, or a shifter. The spring keeps tension on the barrel so that it does vibrate. The picture below shows the frame mounted version.

93980011 by Stuart Black, on Flickr

Here’s the adjuster close up for an XT mountain shifter. The spring (red arrow) goes over the threaded barrel (green arrow) and then goes into the plastic knurled nut (yellow arrow).