I've noticed on a few axial leaded electrolytic capacitors that one lead would be a tinned copper and the other steel. Two examples are a Sprague 500D and an Epcos B41691. The Epcos had a steel lead on the neg. end and the Sprague had the steel lead on the pos. end. Any ideas why a mfg. would do this? Is it just to save a buck? If so why use copper at all? Just curious if anyone has a clue. thanks