German Wheel Meaning

(circus arts) An apparatus made up of two large, usually steel rings joined together by a set of parallel steel bars.

Example: Used other than as an idiom: see German,‎ wheel.
Big Top For Your Head, Orange Coast Magazine, February 1997 - Page 36
  First is the German Wheel, two metal hoops six feet in circumference, joined at six points. Inside, gymnast Chris Lashua rolls, turns and spins through a series of gravity-defying somersaults and acrobatics.