This is a compact PET bottle opener.
The other day I hurt my wrist and can't open the PET bottle cap, so I decided to make it.
https://youtu.be/65JApkwoHAc

[news] In August 2020 I designed a new opener. Here you can attach with a lighter force. Please download it and try it. https://www.thingiverse.com/thing:4570640
I usually use this new version. I also give new version to the people around me.

[requirements]
-small force attachment
-no slipping turn
-compact
-easy to distinguish the front and back

[idea]
-Angled fin structure.
-Center hole (can be pushed with thumb when removing)

[print conditions]
-ABS/PLA
-no support

[How to use]
-Open ... Insert the opener into the cap with the dented side down and turn it to the left (ccw).
-Close lightly ... Insert the opener into the cap with the dented side down and turn it to the right (cw) until you hear a ratchet sound.
-Close tightly ... Insert the opener into the cap with the dented side up and turn it to the right (cw).

[ revision ]
2021/12/23
I deleted two files. "petbottle_opener_release1.stl" and "petbottle_opener_thin_release1.stl".
These files are special and only useful in situations when the thickness of the fins is printed thinner. If these are printed with an accurate printer, the performance of the opener will be poor.
To avoid this, I decided to remove it.

2021/03/03
I add a .step file (PetBottle_Opener_fin08mm _release1.step).
I hope you can remix what suits your needs.

2020/03/02
I add new files(petbottle_opener_08mm_release1.stl, petbottle_opener_08mm_thin_release1.stl) those are thin fin type.

I noticed that the thickness of the fins varies considerably with 3D printers. Therefore, I designed the fin with the thickness changed from 1.1mm to 0.8mm. If the printed fins are too thick to work well as an opener, try the 0.8mm version.
If you are using a printer that performs well and can print accurately, use this 0.8mm version.

2019/11/18
I add a file(petbottle_opener_thin_release1.stl) that is thin type.
This is probably more convenient to carry in your bag or pocket.