Record Mats In Combination With Weights

Fuzztone, the Sota reflex clamp is tightened by turning a nylon grub screw inside the collet clockwise with a 1/8" allen wrench. 

This is not that complex a situation. The purpose of a mat and weight/clamp are to dampen the record so that it does not resonate under the stylus. This dampening has to occur over the entire record surface. A flat mat and a weight just supports the record at the label and rim. The playing surface is up in the air. A mat that is smaller in diameter than the record and has a recess under the label will support a record under it's playing surface except there is no such thing as a perfectly flat record and a weight will not fix this regardless of it's weight. Reflex clamping where a thin washer is placed over the spindle and a clamp that presses down on the perimeter of the label only forces the record into the mat flattening it. For this to work well the mat has to be firm, perfect is the same hardness as vinyl. Kuzma and SME use this type of clamping and the Sota Clamp works this way as do a few others. Excess weight will wear out a bearing prematurely except for those that use a magnetic thrust bearing. Vacuum clamping is the best but complicated and reliability issues may arise with vacuum pumps. Noise is no longer an issue. The pumps are now very quiet. 

In short you want a firm mat 11 3/4" in diameter with a recessed label area and either a reflex or vacuum clamping. The weight of a reflex clamp is inconsequential.   

mijostyn
Why are you telling me? I've done it.
The key is grinding down a brad for a push pin.
Currently experimenting with Origin Live mat over Counterparts held by Sota Clamp with fo.Q tape on foam.
For me another benefit of the reflex clamp is that it grasps the spindle so I can start the spin on the heavy platter to ease stress on belt.
First belt (without procedure) 1 year.
Second belt (with) 35+ years.

I use a concave copper mat with center weight and an outer ring. The sound changes are significant, specially in those old records that are not totally flat, almost as good as the vacuum system in my Bergmann Galder.

The purpose of a mat and weight/clamp are to dampen the record so that it does not resonate under the stylus.

It is a lot more complex than that.
If you have a reflex clamp or heavy weight with washer under the label, then you are coupling the record to the platter or platter mat.
A concave platter/mat with centre weight/clamp  achieves the same.

Many aftermarket weights with a flat surface/no washer are doing nothing .

Excess weight will wear out a bearing prematurely except for those that use a magnetic thrust bearing. 

Unless you have a high mass platter bearing specifically designed for the additional weight.

Before setting up the Soverign I used the Gravity One on my old table. It was no contest. MUCH better truth of timbre, greater dynamics, impressive detail, extension, just more of everything you want and none of what you don't.

Hyperbole to the extreme.
The Gravity is just a lightweight tuning device that sits on the record.
It does nothing to flatten records, or couple them to the platter surface.
They would have you believe that if you put a piece of flooby on the record label it will improve the stylus performance  2 inches away on the first track. A 1/2 cup coffee or a lump of your childs playdough sitting on the label could be just as effective.

I have heard the Gravity on a variety of turntables - it is garbage, a con.
For comparison i have in house weights/refelx clamps from Final audio, Micro Seiki, Sota, Goldmund, Audiocraft and many others. I laso have a variety of mats in the house from Final audio, Micro Seiki, SAEC, Godlmnd, Sota, Seisin, Sumiko and many others.

When I heard the Gravity we tried it on a variety of mats and turntables.
Yes it slightly altered the sound, improvement - no,.

The worst record weight I have ever heard was the much vaunted "Stillpoints" - again tried on a variety of turntables and mats - worse than useless, although it added a little sharpness it muddied up the upper midrange lower treble by some degree compared to other designs.

There is no "best" weight or platter mat becuase the outcome of any of these aftermarket products is going to depend on the platter construction of each particular turntable and the tracking ability and sound quality of your particular arm/cartridge/phono combination.
This is why I keep  library of platter mats and weights/clamps on hand. It can be illuminating to revisit them from time to time when I am setting up turntables.
To believe that a specific weight/clamp solution will be effective on every turntable no matter what the construction is illogical and foolish.