I have a 48" heavy glass table top, and the four tiny little cheezie bumpers that are affixed presently to the inner circular ring - do not secure this heavy piece of glass. Do you have thick round silicon disks that I may add periodically or to replace the present four appointments of these non-quality/caliber plastic bumpers?

This is kind of geeky, but it worked for me.
Gather up the following supplies:

1. A tube of 100% clear silicone caulk
2. Two pieces of waxed paper about 6" square
3. 15-20 pennies
4. A board (approx. 8" square x 3/4" thick)
5. A table that you can leave all this on for at least a day (i.e. not your dinner table!)

Lay down one sheet of waxed paper and put the pennies in stacks of two around the edge it to hold it down. Now, squirt a fair amount of caulk into the middle of the ring of pennies (don't get caulk on the pennies). You want a blob about 2" around and a half-inch high or so. Put the second sheet of waxed paper on top of the caulk and pennies and gently flatten the caulk out a little (not too far though). Place the board on top of the caulk and pennies and place a book or other weighty object on the board to hold everything in place.

A couple of days later, peel the waxed paper off, and you should have a flat sheet of silicone that is 2 pennies in thickness. Use a penny (or other coin, depending on what size you want) and mark a number of circles on the silicone with a pen. Cut them out with scissors and they make fine bumpers for a glass top table.

You can probably also go to a glass shop and ask for some similar clear cushions, but those I've seen are harder and therefore I am afraid the glass will slide on them.

Hope this helps,
WallyH