Chances are, if you dont know what these are, you probably dont need them.
But basically they absorb vibration, are used on delicate av equipment, or under speakers to prevent to sound being muffled by your floor.
These are the 'ultra' "A set of four should be used to support a weight of between around 8 and 16 kg (2 to 4kg each)"
i bought them to use with floorstanders that had no spikes, but they were damaged and have been replaced with different speakers that do have spikes.
see ebay item 230371862300 for more info. that is where i purchased them from.
I paid £18 for these, looking for £15 delivered for the lot.
payment via paypal gift or plus fees