A functional reusable cap for plastic pet bottles normally bought with water or soft drinks.
The design features a hole, allowing for the use of a carabiner or rope to be passed through.
I was inspired to make this after having to lug a large bottle around while hiking, after my back pack was full.
Once printed, all you need to do is glue an existing bottle cap to the inside. I recommend some form of epoxy, and not cheaper super glue as it cannot withstand being twisted.
Using the existing bottle cap ensures your drink remains food safe, and widens the possibilities for different printing materials to be used.