Rocket produced 60 duro Hop-up rubber. These buckings have a molded rounded hump nub inside. The bucking is suprisingly strong for a cheap bucking, definately worth checking out if you're on a super tight budget.
The durometer refers to the rubber hardness. The higher the number the harder the rubber is. For high FPS 450+ 70 is often better. For lower FPS 350 FPS 60 is generally better.