For my work bench/outfeed table/ assembly table, I used 5/8 inch bolts. I glued two nuts into the legs using Gorilla glue. Then I added a flat washer and a nut.

The table is rock solid. The floor is very uneven.
Note: The legs are 2x4's trimmed to 3 inches square, glued and screwed together.
Here are a few pics.
Hope this helps.
Mike

 

That is brilliant thanks!

 

I've used several types including the basic bolt design shown however my favorites are the type with the pivoting base since they stay put better on my seriously uneven floor. (I don't know the brand as I bought them on eBay)

 

Know the seller or have a link?

 

It's been a while and the only thing I remember is I bought them used from an individual seller since all the new heavy duty ones I found were pretty expensive (unfortunately I can't even show you a picture of them since they went with my old workbench when I sold it).

 

I did something similar to above except instead of sinking the nut I used T-nuts. Then on the head of the bolt I welded a large washer and ground the weld flat.

 

go to www.grainger.com or www.mcmaster.com and do a search.

 

Maybe a little late but I see Woodcraft has these for $4.99/4 pack.

http://www.woodcraft.com/Product/2001073/10131/T-Nut-Levelers-4-pack.aspx