A Rail Interface System (or RIS) is a system on most modern-day guns, which allow scopes, grenade launchers, foregrips, flashlights, and laser sights to be "snapped in", or screwed into the gun's RIS. A notable gun with RIS features is the Colt M4, a gun with an RIS can be customized to suit certain situations, and to a high-degree. Most guns use the M1913 Picatinny rail standard RIS.