US Patent 10252099 Portable opposably mounted pull up device

A door frame attachment system includes a pair of pivotable arms that can hook onto a door trim, held closed by a spring hidden in a cavity between the arms. The arms are connected to each other by a hollow shaft that allows various handles to be hung from the system. An exercise device includes the door frame attachment system and a handle suspended by a rope that passes through the hollow shaft. The device offers greater portability and attachment security compared to other inventions of this class, and it also provides greater user comfort by allowing the handles to rotate and pivot into a natural position.