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Granite Gear says:
Body Diversity every person has a unique build, shape and size. Your pack should fit accordingly. The latest step in evolving Granite Gear's fit-focus is the Perimeter series. The series introduces an additional element in fine-tuning the suspension system to one's body: Shoulder Width Adjustment with regular and wide settings along vertical daisy-chained webbing. When adjusting the torso height, simply choose which shoulder width and re-secure the clip to the corresponding webbing anchor points on each side. The series also utilizes the patent-pending Re-Fit waist belt to wrap around your hips just right.
The Perimeter suspension system utilizes a durable spring steel rod outline to give the pack ergonomic form. The spring steel perimeter rod works in tandem with a PE board cone to disperse weight effectively and also allows for secure anchor points for the shoulder straps to attach to.