Compression is the system that keeps your headset tight and secure. There are many options for compression. There are Standard Compression System (SCS), Hidden Internal Compression (HIC), and Inverted Compression System (ICS). SCS and HIC are similar in the sense that a starnut is installed into the fork. ICS is unique in the sense that an oversized star nut is used and install into the handlebar. What is all these compression types have in common is that a bolt is used to pull the star nut in and bring tension on the headset.