British spelling vs .45-calibre

British spelling is a noun but .45-calibre is not a noun.

Word	Noun	Adjective	Verb	Adverb
British spelling	Yes	No	No	No
.45-calibre	No	Yes	No	No

British spelling (noun)	.45-calibre (noun)
English orthography used in the UK, Ireland and most of the Commonwealth (characterized by 'analyse', 'centre' and 'useable')

British spelling (adjective)	.45-calibre (adjective)
	of or relating to the bore of a gun (or its ammunition) that measures forty-five hundredths of an inch in diameter