This is a "hat" to put on water bottle caps for an easy grip on your recycled water bottle caps. This is a companion piece to my earlier Carbonator Cap Wrench. If you recycle and reuse plastic water bottles for making DIY sparkling water, you might find this helpful. Make them in different colors to help organize your bottles!The internal bore has a taper that should be matched to the bottle cap you install it on. It should be pointed out that the harder you mash the Water Bottle Cap Wrench onto the cap, the more you collapse the cap onto the bottle (and the harder the cap grips the bottle), so there is some finesse and balance required to get this Thing to work gracefully.