parallel bars
Refers to the gymnastics apparatus consisting of two parallel horizontal bars.
体操選手が平行棒で演技を披露した。
The gymnast performed a routine on the parallel bars.
平行棒 is the parallel-bars apparatus with two parallel rails, whereas 鉄棒 is the single horizontal bar used for a different gymnastics event.
uneven parallel bars
Compound of 平行 (parallel) and 棒 (bar), directly describing the apparatus.