A specification can become awkward to read when 250 ends one line and GB starts the next. A short reference such as AB-12 can suffer a similar break at its hyphen. Solve the specific break point instead of inserting manual line breaks throughout the paragraph.

Choose one phrase in a working copy and identify why its parts belong together. For a measurement, the value and unit should remain visibly associated. Do not make a long sentence unbreakable merely because a single phrase needs that relationship.

Replace the break point deliberately

Word normally allows a line break at a space or hyphen. A nonbreaking version keeps the joined words on one line.

In desktop Word for Windows, replace the relevant ordinary separator using Insert, Symbol, More Symbols, Special Characters. Choose Nonbreaking Space for the gap between a value and unit, or Nonbreaking Hyphen for the intended short hyphenated group. Insert the character and close the dialog. Check that the original separator was replaced rather than left beside the new one.

For the unit example, keep the digits and letters unchanged. The intended difference is how the phrase wraps, not the number or unit itself. Check a neighbouring ordinary space to ensure the paragraph still has natural places to break.

Test the phrase after the line changes

Add a temporary sentence earlier in the paragraph or make a small temporary width change in the document copy. Inspect the target phrase when it reaches a line boundary, then undo the trial. It should remain readable without a manual line break that becomes misplaced after later edits.

Review narrow table cells and captions separately. Keeping a group together cannot make a phrase wider than its available space fit elegantly; adjust the layout if necessary.

If a reference will be copied into software that expects a literal identifier, test that separate use before changing its characters. A visually similar hyphen or space may not be the exact character the destination requires. Preserve a plain identifier where that function takes priority.

Finally, inspect the delivery copy at normal reading size. Use nonbreaking characters selectively so the important value-unit relationship survives editing without creating large gaps or unexpected wrapping elsewhere.

Sources: Microsoft: keeping words together; Microsoft: inserting special characters.