I made some for my truck out of some 1/2" thick Ultra-high-molecular-weight polyethylene (UHMW) that I had scrapped from work.
I stacked two 3"x3" squares, and mounted them using two galvanized carriage bolts. I cut a concave surface on the top block to match the shape of the spring perch on a table saw by running it perpendicular across the spinning blade. I had to make a special fence that clamped to the regular fence to do that. To get the square shoulder under the bolt head to settle into the plastic, I just torched the head a little and let it melt its way in.
When I have time I want to make a new set with three layers, but as you can see I'll need to buy longer bolts for that.
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:):)