Wolf Tooth Compression Plug with Integrated Spacer Stem Cap Purple. The Wolf Tooth Compression Plug provides an anchor point to set the headset preload on road MTB or gravel bikes with carbon forksessentially securing everything on the steerer tube. A stem cap with a 5mm integrated spacer is included which is important since many fork manufacturers require the steerer tube to extend above the top of the stem. It is available in multiple color options to add some style to your bike.