The black spring in the pic of the 31 above - Camaro discs etc. - is a Posie's Super Slide with the Teflon buttons Itoldyouso mentioned.


The black spring in the pic of the 32 above - Mustang discs, red calipers etc. - is a Durant Mono-Leaf.

The Posie's is as it always was.
The Mono-Leaf seems to be sagging a bit after maybe 9-10 years of use.