These are one-point, two-point, and three-point. Most experts agree that one-point slings are tricky to use and generally not as secure as the other systems. The most common style is the two-point sling, and for good reason. The two-point is regarded as the easiest and most effective type of rifle sling.What is a sling on a rifle?
In the context of firearms, a sling is a type of strap or harness designed to allow a shooter to conveniently carry a firearm (usually a long gun such as a rifle, carbine, shotgun, or submachine gun) on his/her body, and/or to aid in greater hit probability by allowing the firearm to be better braced and stabilized during aiming.