The ball end would be a typical internally threaded screw backing ball. A Labret has a flat end that is fixed (not-removable) to the bar, this allows the front to be attached easily for tragus or lip piercings.
The simplest answer is to measure what you currently have. As everyone has unique ears and piercings we can’t tell you YOUR needs. However, for most piercings, we recommend the “ball-end 1/4″ (6mm)”. Sometimes, 5/16″ (8mm) is worn for deep cartilage piercings or larger ears.
➥ USE CAUTION – Be careful when handling or putting on jewelry as small pieces may easily become lost or damaged.
➥ DRY & CLEAN – Do not shower or swim while wearing jewelry. Occasionally remove and wipe clean with a soft dry towel.
➥ SEALED TIGHT – Jewelry should be kept sealed in air-tight containers to prevent tarnishing.
➥ NO CHEMICALS – residue from makeup, cleaning solutions or other products can degrade the jewelry’s protective coating.