Meaning of expression "cold enough to freeze the balls off a brass monkey

Dear Sir/Madam, A brass monkey is a triangle on a ships
deck that holds cannon balls.Why is it
called a monkey.

Type 'Monkey' into the search box at the top to see our past several lengthy posts on this subject! BTW, there now seems to be no evidence that brass triangles were ever used on ships; thus the question is probably invalid!!