phrases - Is class Xth instead of class X ok? - English Language . . . Generally only if Xth precedes the type in-text I would say 12th day, but never day 12th, in English On the other hand, I would say day 12, but never 12 day (specifically, 12 day would imply 12-day as in a count of twelve, involving the whole span of time)
How do you pronounce xth? - English Language Usage Stack Exchange I personally pronounce 'xth' as ɛksθ Unfortunately, saying ɛkθ simply sounds wrong so I don't suggest that as an alternative If you are reading the expression from a board or a display where the listeners can see it, then you could get away with pronouncing it as ɛks Listeners would tend to fill in the missing sound mentally
“Day X” vs. “Xth day” - English Language Usage Stack Exchange So if you're writing formally, "the fourth day" would definitely be preferred However, if you're writing informally, you could choose whichever one you wanted, as long as you stayed consistent (switching back and forth between "the xth day" and "day x" would definitely be a stylistic error)
Grade x vs xth grade - English Language Usage Stack Exchange Something that I noticed is that Canadians often use "Grade X", while Americans prefer "Xth grade" For example, Canadians would use "Grade 9" rather than "9th grade," while Americans use "9th grade" rather than "grade 9 "
Expressing distance on the road Xth mile or mile X If you're driving on an interstate highway in the US, there are mile-markers that tell you how far you are from the southern and or western end of the highway in that state, so, if you're driving in central Illinois, you can say "You'll see a Ferris wheel on the south side of I-72 at about mile marker 98" (referring to a ride at an amusement park on the southwest side of Springfield, IL)
“20th century” vs. “20ᵗʰ century” - English Language Usage . . . To some extent, it depends on the font you are using and how accessible its special features are If you can do full typesetting, then you probably want to make the th part look different from the 20 part, just like they do here:
punctuation - What is the abbreviation for century? - English . . . FWIW, when I was taught (by History teachers) to take lecture notes as a VIth Form A-level student in Britain in the 1970s, we were taught the abbreviation "C12th" etc as a standard usage (optionally with the C larger than and partially enclosing the number)