This is a spare part for the Ahrend revolt chair. The rubber block that connects the backsupport to the frame deteriorates over time and apparently there is no spare parts availabile from Ahrend anymore (even though they still sell the chair model) I created this piece as a replacement. It is stiffer than the original rubber piece, but it does the job.
I added the freecad model file for completeness as well so if you need to make adjustments it is there for your convenience.
The author marked this model as their own original creation.