Vactar 3rd Syllabas

Our numbers have a specific two-letter combination that tells us how the number sounds. For example 9th 3rd 301st What do we call these special sounds?

Vactar 3rd Syllabas 1

What is the most correct form for 3 in ordinal form: 3rd or 3d? I know both are valid. But I heard that 3rd is something like spoken form and it's grammatically correct to use 3d.

Vactar 3rd Syllabas 2

Ordinal 3: 3rd vs 3d - English Language & Usage Stack Exchange

Vactar 3rd Syllabas 3

When we use words like first, second, third, fourth or 1st, 2nd, 3rd, 4th, in sentences, what will be the best way to write these? Also, what about numbers? Do we put them as numbers or numerals? ...

numbers - First, Second, Third, Fourth or 1st, 2nd, 3rd, 4th? One, Two ...