Supercross forks come with a compression cap that is hollow which allows the steer tube exposed on top of the stem to be covered without using spacers. Grease the compression bolt you have and tighten it while you hold the frame and fork up off of your work surface. Holding the frame and fork off of the work surface while tightening the headset allows the headset to tighten together evenly as it is free of pressure directing it out of alignment. Never sit on your bike while tightening a compression cap.