A quick google search reveals that Mannesmann is a German company that dates back to 1885 and pioneered the manufacture of seamless steel tubing. They still exist today, although mainly in the telecom business.
Brian Samson Vancouver, BC, Canada
http://www.answers.com/
> I believe this is Mannesmann Extra tubing. I don't know the specs,
> but it is quite light. I have a late 40s Benotto made with this
> tubing and it is very nice. It takes a 27.2 seatpost and the bare
> frame weighs 4.8 lb (58 cm). This is a bit lighter than a 64
> Bianchi Specialissima (5.0 lb, Columbus) or a 61 Legnano Roma
> Olimpiade (5.1 lb, Falck), both high-end frames in their day.
>
> Brian Samson
> Vancouver, BC, Canada
>
>
> On 24-Dec-09, at 8:55 AM, John Barron wrote:
>
>> I have an old frame that has a faintly visible stamping on the seat
>> tube. All that I can see are a couple of concentric ovals and the
>> word "EXTRA" sticking out on either side.
>>
>> Does anyone recognize this logo?
>>
>> John Barron
>> Minneapolis MN
>> USA
>>
>> 8" of snow in the first of 4 waves. 20" by Saturday?