I purchased this kit for a bike project that never happened.

Chris King original spacer kit configuration with 1 spacer each of 25mm, 12mm, 6mm and 3mm for a total of 46mm.

Most people will say that it's just a headset spacer.  It is at that, but the machining and tolerances are second to none.  If you are in need of a spacer stack, the fit of these provides a great deal of confidence.