Gear ratio?

[PabloPicasso]

To get a prop on my MD2010 with 120s saildrive I need to know the gear ratio

Are 120's all the same, or is it stamped on the casing somewhere?

 

[Tranona]

2.47:1. Yes they are all the same when fitted to the small engines. If you are buying a feathering propeller such as a Flexofold the supplier will now exactly what size you need.