Air Restrictors are the three-pronged bit that are inside most Nerf blasters. They prevent most of the air from escaping the mechanism, and worsens accuracy. Because of this, Nerfers usually open up their guns and drill them out. This method is called "Blaster Modification", or a "gun mod".
Extensive use of the blaster without the air restrictor can damage the internal mechanism because the air restrictor also protects the internals. To compensate for the lack of this modders place rubber padding to protect the blaster's internals.