8412.21.00 - Linear acting (cylinders)

This HTS category, 8412.21.00, specifically encompasses linear acting hydraulic power engines and motors, commonly known as hydraulic cylinders. These devices convert hydraulic pressure into linear motion, serving a wide range of industrial and mechanical applications where controlled pushing or pulling forces are required. The key characteristic defining this classification is their linear actuation mechanism powered by hydraulic fluid.

Within the broader heading of "Other engines and motors," this subcategory distinguishes itself by focusing exclusively on hydraulic power sources that generate linear, rather than rotary, motion. It is differentiated from its sibling category, 8412.29 ("Other"), which would cover any other type of hydraulic power engine or motor not specifically classified elsewhere within the 8412.21 scope.

The subcategories under 8412.21.00.15 and 8412.21.00.30 further refine this classification based on the construction or design of the hydraulic cylinder. "Tie-rod type" cylinders are characterized by externally threaded tie rods that hold the cylinder together, while "Weld fused type" cylinders have their components joined by welding. The "Other" residual category within these subheadings captures any linear acting hydraulic cylinders that do not fit the specific construction types identified by the preceding codes.