The stamp PT is an abbreviation for platinum, and PT950 refers to the number of parts per thousand that are pure platinum. Platinum alloys are about 90 percent to 95 percent pure; therefore, a higher percentage of an item's weight is made up of the metal.
The number 950 often follows the PT abbreviation, because for alloys of platinum between 850 and 950 parts per thousand, the word “Platinum” must be accompanied by the purity. Platinum is very dense and consequently weighs more than gold. Because of its color, strength and durability, platinum is a common choice for diamond settings, and it is often alloyed with iridium or ruthenium for further strength. Platinum is more expensive than white gold because of its density, purity and longer fabrication time.