Start with the profile, not just the numbers
A 50 × 50 measurement can describe the legs of an angle or the outside dimensions of a square hollow section. Add the profile type and thickness so a supplier can identify the right material.
The separate guides cover angles, channels, beams, structural tubes, pipes, plates, flats and bars. Each guide distinguishes listed dimensions from range-only information.
How common steel sizes are written
Angles are usually leg × leg × thickness. Flats are width × thickness; round bars use diameter; plates use thickness and sheet dimensions. Hollow sections use outside width × height × wall thickness.
Channels and beams are commonly identified by a section designation and sometimes mass per metre. Pipes may be called by outside diameter and wall thickness, or by nominal bore and class. Include the standard or drawing mark when one is specified.
Published options are not a stock list
Size suggestions are transcribed from published manufacturer tables and ranges. They are reference data only: they do not confirm current stock, a particular grade, or delivery availability. Confirm the exact manufacturer and specification in your quotation.
For plates, flats and solid bars, some manufacturers publish dimensional ranges rather than a complete list of every size combination. The reference shows those limits without inventing unlisted combinations; you can type the exact size you need.
Structural sizing still needs an engineer
A catalogue dimension does not determine whether a section is safe for a particular span or load. Use the section called for by the drawing or a qualified structural engineer, then submit that specification for a quotation.