This might be a down-tube lever clamp stop - but IMHO it's too big and is more likely to be a filed-down pump peg.

http://www.bikeforums.net/attachment...7&d=1299077770

There's something vaguely familiar about the 'chunky' lugs, pressed out rear drop-outs and seat stay cap treatment that reminds me of an old 'Cold War' era East German sports bike frame lying somewhere in my heap. Not identical but very similar in lots of ways. Mine is low-end, a cheap export "catalogue sale" bike with steel Thun cranks, Weinmann 500 side pulls, Huret derailleurs and steel rims. The OP's bike at least has a tubular rear brake bridge, making it at least one step up from mine! I could be totally wrong, anyone got better ideas/info?