Bolt bottle cap / Packing Deaign

It's a not very important but indispensable article.
With the trend toward living more convenient,people after exercise which can buy a bottle of mineral water to drink anytime,but when you open the mineral water, often can't find a place to put caps,afraid to drink in our hands inconvenient to stain,put it anywhere afraid to lose
This time lock in the bottom,when drink mineral water is not afraid of two things happen
In addition when the space is small,also can overlapping placed,not occupy space and collapse,also convenient to pack.
Creating a convenient and environmentally friendly design.