BIGGG caps

Hi All,
          this afternoon I staggered in my door after getting back from 
portugal and *wow* a pair of huge caps had appeared.  On closer inspection 
they are 3000pF but no voltage rating.  They look like stand-offs with the 
capacative elements rolled over the outside of the porcelain.  They are about 
4" diameter and 8" high with some M6 lugs at the ends and middle to connect 
to each side of the cap.   
Any ideas for voltage rating folks? 
If it helps they came out of an induction hardening machine.

Pumpin' the MV in GB
Nick Field