An adaptor bar includes a retractable tube unit. Two end parts are respectively connected to two respective ends of the tube unit. Two C-shaped hooks are respectively fixed to the two ends of the tube unit. Each hook includes a first connection portion. Two plates are respectively connected to the two end parts. Each plate includes a first section, a second section and a third section. The second section is formed inclinedly between the first and third sections. The third section of each plate is fixed to the end part corresponding thereto. The first section of each plate is removably engaged with the first connection portion of the hook by sliding the end part. The first section includes a first recess and a second recess. The second recess is located close to the second section and includes a recessed reinforcement which reinforces a portion between the first and second sections.