Is the the later type table with flat section on the leg?
If so, the base unscrews from the table top, revealing a nut welded to the back of the plate. If it is the nut that is stripped, then it wouldn't be too difficult to remove with a grinder and weld a new nut on. Similarly, the hand screw is available from brickwerks - it is retained with a spring clip however, which may need replacing too.
Hth
Mark
1989 1.9TDI (AFN) California
1990 2.1MV Syncro Atlantic
The coating is zinc. Be very careful welding it, as the fumes are poisonous. Best bet is to cut/grind the old nut off, and then clean off the zinc where the new nut is going to be welded. Once done you can paint with galvafroid or zinc hell, or some other zinc rich cold galvanising paint.
Cheers
Mark
1989 1.9TDI (AFN) California
1990 2.1MV Syncro Atlantic