It's a small flanged tube of white nylon (at best) that's not made for bikes, but happens to be unimprovable for taking up the space in an allen-fitting fork crown or seat stay bridge when you have to put a nutted-style brake in there. We sell maybe three of them per year, and if you buy one and for whatever reason it doesn't work, please let us not hear of it. The picture shows what it does, what it is, how to use it...and from this point, you're on your own.
