The Osprey rubber grip is a useful item to have in your tool kit when working with pens. You can use it to pull out the nib and feed from the housing, without damaging the nib or the feed, when the nib is friction fit into the housing/collar. It provides the extra grip useful in performing this action.  

Approx 55mm / 2" X 20mm/0.75" in size.

Note - This accessory is part of the Nib Block kit when you purchase a Zebra G Fountain pen.