Tamper-proof cap ring 28 (28 indicates neck diameter, i.e. outside thread diameter in millimeters)
Size: 21.6 - Ø 31.8
Color: white
 
This cap is equipped with a tamper-evident system to prove that the bottle has not been opened between the time it is packaged and the time the end-user opens it. 
 
How does the capsule tamper-evident system work?
Once the cap has been fully screwed on, as soon as the bottle is opened for the first time, a small circular Polyethylene (PP) ring will detach from the bottom of the cap and attach itself to the neck of the bottle.