On the nail

 In her novel The Case is Closed in the "Miss Silver" series, authoress Patricia Wentworth uses this sentence: "The Mercers would have to eat, and unless they went out and shopped for everything themselves, and paid for it on the nail and carried it home, one or other of these food shops would have their address."

The phrase "on the nail" is not one that is used commonly in American English. It means "immediately or without delay," similar to our common expression "cash on the barrelhead."