Equipment rack with hollow tubes.

 It is for vibration and so the metal does not ring. It works really well for turntables. I use a VPI turntable stand filled with sand for my ClearAudio Inovation Wood  turntable. For tube gear I prefer maple. I went from a SolidSteel rack to a Zoethecus rack and amp stand. It made a big difference especially for my amp.

lostbears...Oh ok so it is for vibration more so for TTs... Thanks

In addition to damping ringing of the metal, it provides more mass, which many believe helps dampen vibrations and unwanted resonance. 
Sound Anchor uses sand to fill their very well-made steel stands.
Star Sound sells Micro-Bearing Conductive Steel™ ball-bearing steel fill material that they use in their own highly-regarded stands, and that they previously used in cables they made.
Core Audio Designs uses lead shot, clay, and sand in their racks.
Some people use lead shot alone, which I have never tried.  You would want to be sure the lead is used in a sealed chamber, such as the sealed legs of an equipment rack, so the lead is not exposed or allowed to migrate to areas where it could be ingested or inhaled by humans.

It is for Vibrations and damping it does work my Rix Rax is filled with Silika sand.Do this asap or ask more questions.