So to anyone wondering where the phrase "freeze the balls off of a brass monkey" originates, a monkey was a term for a metal plate with holes that cannonballs would rest in to keep them rolling about. Since brass and iron have different rates of expansion during temperature swings when it got really cold the plate could shrink enough to cause the cannonballs to no longer fit in the holes and pop out.
So to anyone wondering where the phrase "freeze the balls off of a brass monkey" originates, a monkey was a term for a metal plate with holes that cannonballs would rest in to keep them rolling about. Since brass and iron have different rates of expansion during temperature swings when it got really cold the plate could shrink enough to cause the cannonballs to no longer fit in the holes and pop out.