Originally Posted by
Junk083
The serial number starts with M, so I believe that means 1980-81 Trek 412, unless you have anything else to look for!
I just picked up a very similar frame, with serial number: M4G0XXX
M = 412 or 414
4 = 24" (61 cm ctc, 58cm top, 44.5cm stays)
G = July
0 = 1980
The only difference between the 412 and 414 that year that I could discern was the crank, seat post and toe clips:
http://www.vintage-trek.com/TrekBrochure1980.htm.