Body Jewellery is designed to be removable, therefore balls and ends

do have the ability to loosen/unscrew.  

So don't forget to check them regularly 

Push fit jewellery - the decorative end will have a small rod - this inserts into a small hole in the bar/labret. Check that its fully pushed in.

Clip in - the ball has two small indents which pop/click into place.  

Hinged - the small opened part should click into place when closed ensuring a smooth finish.

Torque/Twist close - should be a seamless loop, gentle pressure in opposite directions should correct if not.

Internally Threaded - this is the type of jewellery we pierce with.  The ball/decorative end has a small threaded rod which is inserted into the main part of the bar/labret/horseshoe and tightened.