A firing pin or striker is a part of the firing mechanism of a firearm that impacts the primer in the base of a cartridge and causes it to fire. In firearms terminology, a striker is a particular type of firing pin where a compressed spring acts directly on the firing pin to provide the impact force rather than it being struck by a hammer. The terms may also be used for a component of equipment or a device which has a similar function. Such equipment or devices include: artillery, munitions and pyrotechnics. Firearms The typical firing pin is a thin, simple rod with a hardened, rounded tip that strikes and crushes the primer. The rounded end ensures the primer is indented rather than pierced (to contain propellant gasses). It sits within a hole through the breechblock and is struck by the hammer when the trigger is "pulled". A light firing-pin spring is often used to keep the firing pin rearward. It may be termed a firing-pin return spring, since it returns it to the unfired position. In semi-automatic firearms, this prevents premature firing from the inertia of the firing pin as the breech mechanism closes in the reloading part of the firing cycle. Firing pins of this type are often too short to contact the primer when the hammer is resting against it. This is a safety measure to prevent discharge from external forces such as a drop. Firing relies upon the transfer of momentum from the hammer to give the firing pin sufficient impact energy to cause firing. Type of cartridge The two main types of metallic cartridges used in modern firearms are centerfire and rimfire. In centerfire cartridges, the primer is located in the center of the base of the cartridge. Firing pins for centerfire cartridges usually have a round cross-section and their movement is usually through a hole in the breechblock along the axis of the center of the barrel's bore. Rimfire cartridges however, must be struck on the base about the rim of the cartridge. While rimfire firearms may use a firing pin with a round cross-section, it is common for them to be flat, with a square or rectangular cross-section and a blunt chisel point. Flat firing pins can be stamped from flat metal stock and usually operate in a slot cut in the breechblock (rather than a hole) that is parallel but offset