Right arm only. The entire cast is approximately 15 inches long. The opening for the upper arm is just under four inches. The opening for the hand is just under 3 inches. The cast is hard, but has some flexibility. If your hand is slightly larger, you can flex the cast slightly to spread it to accommodate your hand. It might spread up to an additional 1/2 inch. This is of costume quality. Sized for an adult or teen, in most cases. The back side of the cast is removed for application to your arm. We suggest you wear it in a sling and hold it to your chest or abdomen to enhance the illusion.