This is a product that will help in the DCC install world. On some installs you need to solder a wire to the frame of the locomotive. This can't be done with good results. The solder will not bond to the metal frames of the locomotive. This is a silver conductive epoxy that will bond the wire and make contact electrically.
NOT cheep but it does work. $30.00 for the two parts of mix.
Here is a link to the manufacture. <!-- m --><a class="postlink" href="http://www.mgchemicals.com/products/8331.html">http://www.mgchemicals.com/products/8331.html</a><!-- m -->

Interesting, but expensive! My first thought would be to drill and tap a screw for fastening a wire to something i can't solder to. But, I can think of a few applications where even a screw is not possible.

Sure!! NOW I find out about this stuff I needed it for a few light sockets at work a month ago... They've been assimilated into my "Parts Bin" now, since work bought new replacement ones

Guess I should have posted this a month ago- would have saved some light sockets.
The product is pricey, but when you need to have something attached to the frame this sure beats trying to solder. In N scale installs there is just is not enough room to drill and tap even a 00-90 screw hole.
Has worked many times for me