What is the fineness of gold at which the threshold for theft, which is a quarter of a dinar (one and a quarter grams of gold), begins?

The threshold for amputation in the hadd (punishment) for theft is one-quarter of a dinar of pure gold, based on the saying of the Messenger of Allah, peace and blessings be upon him: "A thief's hand is not to be amputated except for [stealing] one-quarter of a dinar or more." What is considered is a pure quarter-dinar or three pure dirhams, or their equivalent value.