The new multi-use Trekking Pole Attachment was designed to fit a lot of packs, but specifically it works great on the PFV, Gear Vest, Gear Vest Pro, Vest Pack 2, and Double Barrel. 
 
Note that the Gear Vest Pro is the only pack with attachment points to put these on the front, the rest of the packs these need to mount on the back.
 
Sold as a pair. We use either a pair per pole, or a pair per two poles depending on the mount.