There are some nitrogen filled gas springs that I'm working with that vary in different force sizes. For example, some are 200N in size and some are 280N in size. My question is why do they have different ranges in how much force can be applied? 

Let's say that the 200N has a force that can be exerted from 8lbs to 32lbs but the 280N is from 32lbs to 59lbs. Why is there a range difference.