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.

I added sand into the hollow metal tubes of my racks. The available holes in some parts were very small. so I made a small stuck on funnel out of clay...  then sealed the holes with liquid polyurethane. That was over twenty years ago. I still like the racks and have no plans on upgrading etc.

@elizabeth  Would it be worth adding the sand even though i dont use a TT. ? I dont have anything special as far as racks that i have. In fact they were very cheap. But i did go to a granite wholesaler and got 5 pieces of 2 in thick granite cut and using them as platforms for my ARC Ref 6 on one rack , another granite platform for my Rega Isis cdp on the other rack, a granite platform for my Krell FPB 600 that sits on the floor. And 2 granite platforms to put under my B&W 800 Matrix speakers. Also using for now Vibra cones and pucks for my preamp and cdp. 

Hollow metal can ring a lot. Filling with sand will stop that totally.Some folks use fish tank quartz, I used cheap sand box sand, but I had to dry it on the stove to remove the water.

I bet you can’t hear hollow tubes ring even when you put your ear right up to them. It’s an old wives tale. I know what you’re thinking - but if I strike the hollow tube with a small hammer I can hear it ring. Solution: don’t strike the hollow tube with a small hammer while music is playing. 😛 Sand filled speakers never really caught on either for the same reason. If you’re determined to prevent ringing more elegant solutions include wrapping 2” length of the tube with viscoelastic tape or sending the tubes in the cryo lab and/or filling about 1/8 of the tube with hollow fiber wool.

@elizabeth @geoffkait .....Thanks...... I just did the test with a small hammer while i had my ear on the tube. I did not hear any ringing. I just heard a little bang from the hammer. Maybe it depends on how thin or thick the tubes are. If i did hear a ringing i would of filled them with sand also. But since i did not hear a ringing i will just leave as is.