Originally Posted by 9volt

Is it a 21" frame?


A. Serial numbers beginning with M or N (41X and 61X bikes or frames) seem to have a different meaning for what normally is the year digit. The year digit is the fourth character in the number. In the 50 M and N serial numbers that have been sent in by owners, the year numbers go from 0 through 9. The remaining part of the serial numbers seem normal.



According to the brochures, Trek did not make 41X and 61X bikes or frames during 76, 77, 78, and 79 and also not in 83, 84, 85, 86, 87, 88, or 89. These serial numbers apparently do not follow the year convention used for other Trek models. It is likely these frames, SNs beginning with M or N (Models 41x and 61X), were contracted out or were made in a separate Trek facility, and were given the old serial number form so as not to interfere with the sequential numbers being assigned by Trek in their main shop, which began in late 1980.