This article is from the Piercing FAQ, by Anne Greenblatt with numerous contributions by others.
Straight and curved barbells are measured by the linear width from
ball to ball. Circular barbells are measured by the inside diameter.
Straight Barbell: A straight bar with a ball on each end.
Curved Barbell: A curved bar approximately one quarter of a circle.
Often used in navel piercings or when an unobtrusive piece of
jewelry is desired. Also used when the width of the piercing
requires such a large diameter ring as to be uncomfortable. Curved
barbells are sometimes called L-Bars or Half Moon Barbells or Banana
Bent Barbell: Bent Barbells usually refer to barbells bent at an
angle, not curved. Because the bend limits movement of the jewelry,
bent barbells are not appropriate for new piercings.
Circular Barbell: A circular bar approximately three quarters of a
circle which can be worn in piercings for which a captive bead ring
is appropriate. Circular barbells are heavier than captive bead
rings and hence may not be appropriate for all new piercings. A
captive bead can be inserted between the balls for aesthetics or to
prevent losing the balls. Circular barbells are sometimes called
Horseshoe Barbells, although some manufacturers make Horseshoe
Barbells that are U-shaped rather than circular.
Slave or Banger or Captive Barbells: A captive bead ring is
attached to one or both balls of a straight or curved barbell or
Labret. Because of its weight, this design is not appropriate for
new piercings in which the ring portion is worn. This design may be
appropriate for new piercings in which the barbell portion is worn
depending on the location of the piercing; the ring can also be
removed to allow the piercing to heal.
Barbells in complex shapes: Barbells made in complex shapes are
often not appropriate for new piercings.
Barbells are manufactured with one of two thread designs:
Internally threaded: The bar is threaded internally and the ball
screws into the bar post. The edge of the bar post should be
slightly rounded to ease insertion. A guide wire or taper can be
used between the barbell and needle to aid insertion. Most
internally threaded balls are made by tapping threads into a
drilled ball. A few manufacturers make solid one-piece balls that
are made from a single piece of metal. Couterbored or countersunk
balls are bored around the threads so that the ball overlaps the
end of the bar post.
Externally threaded: The bar is threaded externally and the bar
screws into the ball. The threads can damage the interior of the
piercing during insertion; the threads can get caught on the
interior of the piercing, making insertion difficult and
painful. The threads can irritate or damage even a healed piercing
when the jewelry is changed. Some externally threaded jewelry is
designed so that the threads can be inserted into the end of the
needle, preventing contact between the threads and the piercing.
Threading style and dimensions vary between manufacturers and are
often incompatible. Replacement balls should be purchased from the
Barbell ends are not limited to balls. However, certain barbell ends
such as spikes, skulls, dice, and other complex shapes are often not
appropriate or comfortable in new piercings because of their shape and
The threads of internally threaded stone balls are usually affixed
using an epoxy and should not be worn in tongue or genital piercings
because the epoxy can deteriorate and weaken when exposed to saliva
and urine. Additionally, stone balls can shatter when accidentally
bitten, particularly if the stone is brittle or porous. Soft stones
such as tigers eye and jaspers should not be worn in tongue or genital
piercings because saliva and urine can erode the stone. Malachite,
turquoise, and lapis can leach copper in these environments. Lesser
grades of brittle stones which are easily chipped should be avoided.