Hi Eric,
I believe the "tooth" is meant to help locate the dropout as well. Check out the CR link listed below. It explains and shows the Claud Butler version of the tooth and is quite large.
http://www.cyclesdeoro.com/
Best Regards, troy warnick
>From: "Eric Elman" <tr4play@home.com>
>To: <classicrendezvous@bikelist.org>
>Subject: [CR]Simplex DO Question
>Date: Tue, 16 Jan 2001 17:23:07 -0600
>
>I have what I presume to be a 1970 Peugeot PX-10 frameset based on decals
>and date stamp on rear Simplex derailleur. The left rear Simplex dropout
>is
>odd - can anyone tell me more about it? Hanging down from the front edge
>(section of metal which the axle would rest on) is a 3/4" tang protruding
>down from the leading edge. It's about 1/4" wide at the top and narrows to
>a gentle point - sort of the shape of a sharks tooth. Sorry, but I don't
>have access to a digitle camera at the moment so I can't help with jpegs.
>Is that enough for anyone to have ideas of what it's for, when it was used,
>etc.
>
>As always, thanks in advance,
>
>Eric Elman