It is an adjustable valve that can be adjusted by the adjuster on the end to slow down or speed up the return of the clutch arm. For drag racing when you dump the clutch instead of it hammering into full hook-up, you can slow it down to engage in a smooth motion. This saves wear and tear on the tranny during launch, but it also slows down engagement during shifting all other gears too. So using this method I have to give up something (fast 2-4 clutch engagement) to get what I want which is to slow down clutch hookup on launch. Really not sure how much slower the engagement will be for the 2-4 gears but will have to play with it abit to get it right.
Kevin