Pipe/tube sizing
Typically expressed as outer diameter (OD) and wall thickness, sometimes with a nominal bore reference for pipe specifically. See our wall thickness guide for why both numbers matter, not just OD.
Sheet/plate sizing
Expressed as thickness (gauge or millimetres) plus overall sheet dimensions (length x width). Thickness notation can appear as gauge number (an older, less intuitive system) or direct millimetre measurement — ask your supplier to confirm in mm if a gauge number isn't clear to you.
Bar sizing
Round bar is sized by diameter; square/flat bar by cross-section dimensions (e.g., width x thickness).
Tolerances
Manufacturing tolerances mean actual dimensions can vary very slightly from nominal size — normal and expected, not a defect, as long as within standard tolerance ranges. If a project has an unusually tight fit requirement, flag this explicitly when ordering.
When in doubt
Describe your application rather than trying to specify a size chart number yourself if you're unsure — we'll confirm the right dimension for the job.