What are the circular discs people use on components?

Damping plates. Several companies make them, including HRS and Artesenia. Supposed to damp resonance in the chassis. Years ago people put bricks on their components supposedly to make things sound better. Never tried them myself, so I have no opinion on their effectiveness or lack thereof.  Probably a few people around here using them, so you’ll likely get some input. 

Amazon, door weights to hold the door open

are these really necessary?

Yes. They are very necessary. Buy as many as you can afford.

I 2'nd the door weights on Amazon. They are actually called door stoppers. Type in the search bar : Stainless Steel Door Stopper (3 Pack). I use them with great success. Enjoy ! MrD. 

Are you referring to the Combak tuning disks that were popular back in the 80s and 90s (and for all I know, today)?  They were gold-colored circular discs.  They did not damp things, but supposedly tuned resonances to a different frequency.

Most people use the door stoppers not for any "resonance" damping, but merely (as John Darko showed in many of his YouTube videos from two years ago) to hold lightweight components like streamers and DACs in place such that the weight of the cables doesn't pull them off the shelf or hold them up at a flaky angle.  Yeah, the weight would likely lower the frequency of any resonances, but your mileage may vary on that. They are a cheap fix and don't look that bad. 

Interesting for sure. Does anyone have any advice as to the amount of weight one should use? I assume it’s more for heavy amplifiers and less for lighter components  

If you've got circular ring above your component, then you're probably not in this world anymore.

I hope the people who buy these remember to check the blinker fluid in their cars.

@fthompson251 those are them ! 

So basically the discs are pretty much worthless.

I still wish there would begin designing more racks that have casters. I use a customized rack made from steel that comes with casters, from anchor.  It's well-made extremely solid and was really quite reasonable pricewise.  i think it’s insane to put a 150 pound amplifier on a rack that does not move and requires two people to help out.

How cool it would be to design a lift for internal use that you could wheel around to move amplifiers and speakers. Like the lift they use on the back of a pick up truck when they quickly move Indy cars from the road when they crash but of course on a different scale and separated from a pick up truck.

OP, both of your last comments are simple to solve, as the 'tech' involved was sorted out decades ago....just not applied by anyone....

See y'all on GoFundMe....😏😎👍