Karats Plumb – When you see a “P” after a “K” mark on gold (such as 14KP), it means that the gold has been measured and confirmed to be exactly 14 parts of 24, pure gold. Typical K marks (10K, 14K, 18K, etc.) indicate the gold is close to or at that amount. For example, a piece of jewelry marked 18K could actually be 17.75K, or 17.75 parts of 24.
The KP stamp starting showing up on jewelry in the 1970’s when the US government updated the National Gold & Silver Marking Act, defining tolerances for gold containing items. Prior to then, an item marked 14K could be anywhere from over 13K to under 15K. The KP mark was a way to ensure that buyers knew their gold jewelry had been tested to be exactly the karatage stated.
As of when the changes went into effect in 1981, items have to be within 3/1000ths of their stated karat value. So 14k (which is 58.5% gold) now means the item is at least 58.2% gold. The KP mark became obsolete at that point.