These are the codes used to describe driven and undriven axle combinations on train sets. The first letter refers to the number of driven axles, the second to the number of trailing axles.
Ao=1, Bo=2, Co=3 and so on. Numbers mean unpowered, or trailing axles.
So for example, the NS1800 is classified as Bo-Bo. This means two bogies, each with two sets of powered axles:
The NS1200 is classified as Co-Co. This means two bogies, each with three driven axles:
The SGM Sprinter 3-car is classified as Bo-Bo + 2-2 + Bo-Bo. This means six bogies (two per car), the front and rear two both have two powered axles, the middle carriage has two trailing axles:
