off the rack
Of clothes, mass-produced and ready to wear. Often hyphenated. Primarily heard in US. You can find really stylish clothes off the peg, if you look hard enough. Don't show up to the interview in some off-the-rack suit—you need to spend a bit more money if you want to impress them.
off-the-rack
Off-the-rack clothes are made in large numbers and sent to shops, not made specially for a particular person. We want to improve the fit of off-the-rack items. Note: You can say that people buy clothes off the rack. He was wearing a blue two-piece suit that had obviously been bought off the rack when he was several pounds lighter.