A pinned and welded flash hider is a device that is attached to the muzzle of a rifle in order to reduce the visible signature when the weapon is fired. The flash hider works by dissipating the gases that are released when a round is fired, thus reducing the amount of light that is seen. In most cases, the flash hider will also have some sort of baffling system in order to further reduce the visible signature.
There are a few different ways to attach a flash hider to a rifle. The most common method is by means of pinning and welding. This involves attaching the device to the muzzle via two small pins, then welding it in place. This method ensures that the flash hider cannot be easily removed without damaging or destroying it.
Another way to attach a flash hider is by means of threading it onto the muzzle. This allows for easy removal and installation, but does not provide as secure of a hold as pinning and welding. It is also possible to permanently attach a flash hider by means of machining it directly onto the muzzle (a process known as machining in place). This provides an extremely secure attachment, but makes removal very difficult (if not impossible) without damage to either the firearm orflash hider itself