I found this unembossed insulator at a flea market yesterday. It looks like a CD 105 but its quite a bit larger. Possibly a Pennycuick style. Could this be a previously unknown style? Let me know what you think.

5-27-09 UPDATE: I have received many responses and the majority believe that it is a CD 126.3 made by Oakman or American Insulator Co. Thanks for the many replies and helpful information.