Yup. Ding ding ding. We have a weiner!
Also referred to as 'spring rubber' for you Nascar fans. Place between the coils to change the spring rate, can aid in cornering, and firm up the ride. With the new endlinks on the front, and new coming soon for the rear, I won't use them. Our springs are variable rate coils, anyway, so these little suckers would all have to be different sizes to work.
They also make a twist in aluminum style. I've had these for quite some time, playing around with the idea.