let's you change velocity w/out removing cocking rod
Basically this allows speedier and easier velocity adjustment at the chrono. It comes standard on the Nexus cocker and it's a very nice upgrade. My friend has a cocker he basically built himself and when we have to adjust velocity at the chrono, he's always having to stop and pull everything out and it's just a hassle. With this all you need is a hexkey and BAM! you're done. It's like a tournament adjuster on a spyder except it's for an autococker.
Not a necessity but it does ease the frustration of chrono velocity changing and it makes the time at the chrono go a lot faster, so you can GET IN THE GAME!!