After the horror of being forced to imitate a Huret Allvit with the Schwinn GT100, Schwinn allowed Shimano a bit more freedom with the design of the Schwinn GT120. The GT120 is basically a Shimano Lark STO with Schwinn touches:

1. •A huge bashguard built onto the rear knuckle.
   

2. •An allen key hanger bolt - of no known purpose - it is not a 10mm thread.
   

3. •A larger cable adjuster.
   

4. •A trapped cable clamp bolt - of rather nasty Huret-like design.
   

Shimano did take the opportunity to build-in their latest adjustment screw layout - with plastic shake proofing instead of steel springs.

This example has two sets of date code letters stamped on it (AC and YL) - holding out the promise that it is the Rosetta Stone of the two Shimano year letter systems - but it still does not quite make sense. I think A is 1976 in the ‘new’ system, Y is  1979 in the ‘old’ system. I have gone with 1976.

One day it will all become clear.

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1. •Brand: Schwinn, manufactured by Shimano
   

2. •Country: USA, manufactured in Japan
   

3. •Date of introduction: 1974
   

4. •Date of this example: 1976 (date codes are AC and YL!, ‘elliptical S’ marking on pulleys)
   

5. •Model no: unknown
   

6. •Weight: 366g including hanger plate but excluding drop-out bolt
   

7. •Maximum cog: 28 teeth
   

8. •Total capacity: 28 teeth
   

9. •Pulley centre to centre: 54mm
   

10. •Index compatibility: friction
    

11. •Chain width: 3/32”
    

12. •Logic: top normal
    

13. •Pivots: two sprung pivots
    

14. •Material: steel
    

0339/L