I don't think I know of any classes with more than two inside cylinders...
The red item on the 2nd driving axle isn't a counter weight, but rather a crank. As stated it takes the drive from the inside cylinder. This locomotive has outside cylinders too, but it was common in the UK to have locomotives with just two inside cylinders. I believe the practice was started as placing the cylinders low down and inside the wheels helps with locomotive stability.
The red item on the 2nd driving axle isn't a counter weight, but rather a crank. As stated it takes the drive from the inside cylinder. This locomotive has outside cylinders too, but it was common in the UK to have locomotives with just two inside cylinders. I believe the practice was started as placing the cylinders low down and inside the wheels helps with locomotive stability.