My spikes are fitted into these small metal cups with plastic pads connected to them and felt pads below.
I used Silicone to hold them on, so when I move the speaks to clean they stay on.
Got 'em from the hardware store, cost about $2 for each pack of four. They are about 1/4 inch dia. cups and the plastic disks with the felt is about dime-sized.
It's interesting to note that the vibration transmission through dissimilar materials is better reduced than with the spikes alone.
The spikes will actually "nail" the speakers to the floor eventually, causing much greater coupling than without them.
Alternately, a finished wooden board can be placed below the spikes, if you want greater coupling to the floor.