Positioning device for holding member of sport racket stringing machine

A positioning device for holding member of a sport racket stringing machine, comprising:

• a rack, a contact member, an operation member and a spring, the rack engaged with a top board of the stringing machine and having multiple one-way ratchet teeth defined in a top thereof;
• a holding member having a body connected to a top of the top board and the body having a chamber which is located adjacent to the rack;
• the contact member movably located in the chamber and a lower end of the contact member extending toward the rack and inclinedly engaged with the ratchet teeth of the rack so as to position a holding member;
• the spring located in the chamber and connected between the body and the contact member so as to urge the contact member to be in contact with the rack 10, and
• the operation member pivotably connected to the chamber and being a hook-shaped board, the operation member having a driving portion and a positioning portion respectively located on two ends thereof, a curved operation portion connected between the driving portion and the positioning portion, the operation portion protruding out from the body, the operation member having a pivot at the positioning portion so as to be pivotably connected to the body, a top end of the contact member extending between the driving portion and the positioning portion and being located adjacent to the lower end of the driving portion, the driving portion pivoting the contact member to move the holding member.