Positioning structure of clamper of threading machine for racket

A positioning structure of a clamper of a threading machine for a racket comprising:

• a rack, an engagement protrusion, an operation member, and two springs;
• wherein a fixing holder is erected on a top of a support plate of the threading machine, and the rack is engaged on the support plate, the rack includes multiple first teeth extending from a top of the rack, the fixing holder includes an accommodation chamber defined in the fixing holder and communicating with the rack, and the accommodation chamber has an opening formed on a side of the fixing holder;
• wherein the engagement protrusion is received in the accommodation chamber and includes a toothed extension on which multiple second teeth are formed, wherein the toothed extension is parallel to the rack, such that the engagement protrusion engages with the rack by ways of the toothed extension, the engagement protrusion includes a recess defined adjacent to the opening and includes an abutting fence formed on a top of the recess;
• wherein the operation member is rotatably connected with the fixing holder, and the operation member includes a drive portion and a push portion, wherein a rotary shaft is inserted through the operation member and two ends of the rotary shaft are connected with the fixing holder, such that the operation member is rotated along the rotary shaft;
• wherein a first end of the push portion is obliquely connected with the drive portion, and the push portion partially extends out of the accommodation chamber via the opening, a second end of the push portion extends into the recess and is proximate to the abutting fence, such that the push portion pushes the engagement protrusion upward so that the engagement protrusion disengages from the rack;
• and
• wherein the two springs are mounted on a top of the engagement protrusion, and two ends of each spring abut against the engagement protrusion and the fixing holder respectively so that each spring forces the engagement protrusion to engage with the rack.