The uneven parallel bars or asymmetric bars is an artistic gymnastics apparatus. It is used only by female gymnasts. It is made of a metal or steel frame. The bars are made of wood, plastic, or composite materials. The English abbreviation for the event in gymnastics scoring is UB or AB, and the apparatus and event are often referred to simply as "bars" or "uneven bars".

Dimensions

Measures of the apparatus are published by the Fédération Internationale de Gymnastique (FIG) in the Apparatus Norms brochure.

• Height including about 30cm for landing mats:
• upper bar: 245 cm (approx 8 feet)
• lower bar: 165 cm (approx 5 feet, 5 inches)
• Width of bar: approx 1.5 inches
• Length of the bars: 240 cm
• Diagonal distance between the two bars: 130180 cm (adjustable)

Routines

1. Mounts the apparatus. Depending on the skills of the gymnast and level of competition, the mount may be as simple as a pullover or as complicated as a flip onto the bar.
2. Performs the actual routine, which will include swings and at the higher levels of competition, giant swings, handstands and release elements (skills in which the gymnast lets go of the bar and regrasps it). The gymnast will also be expected to demonstrate at least one bar change, i.e. moving from the low bar to the high bar or vice versa.
3. Dismounts the apparatus and lands on the mat.

In USAG levels 1-6, everyone in the same level performs the same compulsory routine. In levels 7 through Elite, gymnasts make up their own routines within specific requirements.

== Evolution == The uneven bars apparatus originally consisted of men's parallel bars set to different heights. Consequently, the bars were very close together, and gymnasts could transition from one to the other with little difficulty. Routines of the early 1950s chiefly consisted of simple circles, kips, and static balance elements and holds. In the late 1950s the trend shifted toward fluid motion, and gymnasts began to perform routines comprised of more difficult circles, kips, beats (bouncing the body off the low bar while hanging from the high bar), wraps (wrapping the body around the low bar while hanging from the high bar) and transitions. Release moves also began to come into play, although they were almost entirely limited to transitions between the low and high bars.

As other events in gymnastics increased in difficulty, so did the uneven bars. Gymnasts and coaches began tinkering with elements, attempting more challenging dismounts, and adapting moves from men's high bar. In 1972 Olga Korbut pioneered the Korbut Flip, the first high bar salto release move. Nadia Comaneci continued the trend with her original Comaneci salto at the 1976 Olympics and advanced handstand elements four years later. The giant swing, the staple of high bar in men's artistic gymnastics (MAG), was also adopted into the women's Code of Points, and quickly became a basic uneven bars skill.