A leash is a brace and a half

Something I learned today: Brace (two), leash/lease (three), dozen (twelve), score (20), century (100) are known as "secondary numerals". Exclusive numerals (one, two, three, etc) sort of concrete in a language and don't change - the proper English word for "two" is always "two" - but secondary numerals let us play with the language, so instead of two we could have a brace, a couple or a pair. These are also words for sets of a particular number, rather than actual numbers, which is why you refer to them as "a brace" and "a dozen" and why you can count them even though they already refer to numbers - "a leash is a brace and a half", "three score years and ten". Depending on your dialect of English, they have irregular plurals (like deer, sheep and fish), so you have "three dozen", "five score", or "two pair", but several "dozens", "scores" or "pairs". But now I'm wondering if "a pair of braces" is redundant, because "pair" means two and "brace" means two, or if the word "braces" in this context means "something that braces" - as in supports...