peg

off the peg (of clothes) ready-made as opposed to specially made for a particular person. chiefly British

☞ A North American variant of this phrase is off the rack.

a peg to hang something on something used as a pretext or occasion for the discussion or treatment of a wider subject.

a square peg in a round hole a person in a situation unsuited to their abilities or character.

☞ The variant a round peg in a square hole is also found, although it is less common.

take someone down a peg or two make someone realize that they are less talented or important than they think they are.