These Smooth Glitzy Balls in 4mm and 5mm diameter are for internal threaded shafts measuring 1.6mm. They come in Crystal AB and Crystal Clear. The attachments actually have the standard 0.9mm thread. These attachments actually have the standard 1.2mm thread. These attachments will fit internal thread Dermal Anchor Bases, internal thread Labrets, Barbells, Curved Bars, etc. DO NOT autoclave Smooth Glitzy Balls.