Floor protection from spikes

They also come in giant size (which you might want), and regular "cup" shape or with integral thread (lots of different size threads).

What method are you using to attach or put these items under such heavy speakers?    

No method, they are deep dished and with my speakers show no signs of slipping out of the dish as I slide and adjust the speakers across my hardwood flooring. The three variants of the sliders offer a different tone per say, I chose the brass as they were the cheapest and the original purchase was just to assist in the setup. I have also added their threaded jumbo sliders to a Led Balloon turntable stand replacing the pointed cones that came on it stock and love the results. Enjoy the music