KYB TV Episode 10: The Difference Between Monotube and Twin-Tube Shocks 

For truck owners, choosing the best truck shock usually comes down to deciding between a monotube and a twin-tube design. Both shocks work well, and it just depends what type of shocks your truck came with from the factory, and how you are using your truck. If your truck came with a twin-tube shock, then a twin-tube, like the KYB Excel-G will be the correct, performance restoring designed shock. A higher pressure monotube, like the KYB Gas-a-just or MonoMax will deliver additional control and load-carrying capabilities. Some trucks did come factory equipped with monotube shock absorbers, for these vehicles we recommend only ever using a monotube design. The KYB Gas-a-just will be the correct, OE performance restoring design, while the MonoMax will be your performance upgrade option. You can count on the KYB catalog at kyb.com to let you know what the recommended OE design and which part is a performance upgrade.
Monotube shocks and twin-tube shocks work a little differently. A monotube has one tube and the nitrogen gas and hydraulic fluid are separated by a floating piston. This design responds quickly and gives you additional control and damping on demand. Twin-tube shocks are still gas charged, but the gas and oil are mixed in the working cylinder, and while they work great for normal driving, they may not be the best choice if you are using your truck a lot of different ways and are towing and hauling.