on the nail
Allegedly from the tradition of striking bargains by placing cash on the nails in Bristol, Limerick and Liverpool. The Oxford English Dictionary however cites an Anglo-Norman phrase from c. 1360, "payer sur le ungle" to pay on the (finger)nail meaning "to pay immediately and in full", and the Latin "ad unguem", exactly. It quotes parallel usages from 17th century French, Dutch and German sources and adds that "N.E.D. (1906) notes that: ‘the explanations associating it with certain pillars at the Exchange of Limerick or Bristol are too late to be of any authority in deciding the question’."