Hi,
I found a burned varister in an industrial card. Marking says S14-K510. I was able to find a piece in local market which is marked as 14D-511K. Just want to conform if they are the same thing or not? I know the voltage of both are 510V. Does "S14" and "14D" make any critical difference?
[Edit]: Apparently, both varistors are almost same color, shape and size.
Regards.

 

If you don't have access to datasheets, and the new varistor physically fits and has a similar voltage rating (510V), it should work as a replacement.