Note on the sketch 'viton_damping_sandwich.pdf'
Brian Lantz, from an email to Fabrice on Nov 26 2008

Also, instead of glue, I was thinking you could just bolt the damping end of the strut together. Get some thing <= 1mm viton sheet and use it in the shear layer arrangement. I've attached a little sketch. In this picture, the bolts touch the strut side, and so must not touch the pendulum cage side. One side of the strut side is a bolt-on cover plate, stiffer than the viton, with a little flexure element to allow some squeezing variability. Two layers allows the thing to be 2x as stiff as 1 layer. One could stack of more if desired. One can make the piece on the pendulum frame side pretty much any shape. One could also drop little o-rings in the gaps between the bolts and the pendulum frame piece to eliminate accidental shorting between the metal bits. There's no glue, and it's easy to change the amount of viton, and so tuning the stiffness is relatively easy.