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Gossamer Gear says:
A simple top loading shoulder strap pocket that will fit on most any pack.
This simple easy to use shoulder strap pocket, while designed with our hiking packs in mind, will fit on most any pack. Dual zipper pulls and a wee bit of foam to help it hold it shape make it very easy to access your goods. There are one horizontal and 2 vertical attachment points that are adjustable for quick and simple attachment.