Down on the nail, Pay down on the nail. In ready money. In Latin: “Super unguem;” in French: “Sur Vongle;” as, “Boire la goutte sur Vongle ” (see Supernaculum), “Payer rubis sur Vongle, ” where rubis means red wine. The Latin ungulus (from unguis) means a “shot” or reckoning, hence ungulum dare, to pay one's reckoning.
“Quo quibus prisis, et cariagiis pleana flat solucio super unguem.” —An Indenture dated July 15th, 1326 (Scot's Act)
O'Keefe says: “In the centre of Limerick Exchange is a pillar with a circular plate of copper about three feet in diameter, called The Nail, on which the earnest of all stock-exchange bargains has to be paid.”
A similar custom prevailed at Bristol, where were four pillars, called nails, in front of the Exchange for a similar purpose. In Liverpool Exchange there is a plate of copper called The Nail, on which bargains are settled.
(For want of a). “For want of a nail, the shoe is lost; for want of a shoe, the horse is lost; and for want of a horse, the rider is lost.” (Herbert Jacula Prudentum.)