D1 is the rod diameter in millimeters. A larger diameter improves side-load capacity and buckling resistance. Match D1 when selecting an equivalent spring.

D2 is the outer body (cylinder) diameter. It defines overall size and affects force at a given pressure. Specify D2 together with D1 for accurate replacement.

C1 is the working rod stroke — how many millimeters the rod extends when the spring is fully compressed. Critical for lids, hatches and moving mechanisms.

C2 is the overall length in the fully extended state. Use it to verify the spring fits the assembly without interfering with nearby parts.

N1 is the gas spring force in newtons. It determines whether the spring can hold or lift the load. Small tolerance is acceptable; a large difference changes mechanism behavior.