Internal Dimension

Internal Dimension (ID) in foreign trade specifically refers to the diameter or width of the hollow interior of pipes, rings, containers, or mechanical parts, commonly denoted as ID. It is widely used in hardware, plastics, piping, bearings, packaging, and other industries. It is the opposite of 'Outer Dimension' (OD): OD determines the space a product occupies and how it fits with external structures, while ID determines whether it can fit over or allow passage of other objects, directly affecting assembly, flow rate, and sealing performance. Usage scenarios include: inquiry and quotation (e.g., 'Please provide ID and wall thickness'), specification sheets, quality inspection reports, and contract attachments. Precautions: ① Units (mm, cm, inch) and tolerance ranges must be clearly specified, as ID tolerances are more sensitive than OD; ② Distinguish 'ID' from 'internal dimensions' (e.g., inner width × inner height for rectangular tubes) to avoid ambiguity; ③ If the product has coating or lining, confirm whether the ID is before or after coating; ④ Different from 'Nominal Diameter,' which is a nominal size, while ID is a measured value. Accurate ID labeling can reduce return and claim risks.