This is an adjustable length bungy cord assembly that attaches onto the two tabs at the bottom of any Kit Bag and goes around the wearer's back to prevent the Kit Bag from bouncing while running. You won't need it for hiking, you won't need it for mountain biking, but you will appreciate it for runnning. It comes standard with the Runner's and Snubby Kit Bags and is an optional accessory for the other KBs.