Got this beauty from Jim Fielding at the recent TX show.

It's 6.25 inches long, an inch thick, and goes from 2.25"-3 in width.

It's a N'530 on page 10 - http://www.insulators.info/catalogs/lelectroverre/1948/page10.html

Page 11 of the catalog shows some pictures and how they were wired in.

http://www.insulators.info/catalogs/lelectroverre/1948/page11.html

You can also look at page 47 in Crown Jewels April 2003 for information.

Thanks for looking.