Sometimes you just need an individual plate.
Sintered Friction Plates are made with metal and Organic Friction Plates are made with carbon. The Sintered tend to last longer and have a more aggressive "Bite" (you feel it more) and are meant for racing (but work fine on the street). The Organic Plates are more progressive (doesn't engage as harshly as the Sintered) and are meant for road use.
When a steel plate is "Concave" it means it has a dished shape to it like a spring.