[8A51C]

The metre is not used for everything. The standard for construction and manufacturing is the millimetre. In the UK a standard kitchen unit is a 600(mm), with 300 and 900 varients. Appliances come in 500, 600 and 900 widths, that being the gap or unit they (should!) fit into. It would feel unatural to me to say 0.6 etc for a unit. These common dimensions are used like nouns, "You need 3, 600s" rather than "You need 3 units 600mm wide" tying them more closely to language and perhaps then harder to change.