those are adjustable machine pedatels and those black things are really cheap and good for making those. Those things absorb vibration and are bit elastic so one could not tought better pieces for making those machine feets. Those cost somethin like 1€ in here.
Pete, You're a winner tonight Those are really cheap and useable in everything you need absorbation and flexibility. We use them in rally cars motor mounts, machine pedastels etc... Or not in all the machines and cars. Only cheap ******** like me use them