what KP on your wedding ring set doesn't mean is: Karat Plate! KP stands for Karat Plumb.
This mark was introduced in the US in 1978. Legally the karat could vary by 1/2 carat so as you could imagine when a manufacturer had a choice of 8 1/2 kt instead of 10k... well he might be tempted. 10 KP is a guarantee from the manufacturer that the metal is no less than 10 karat gold.
