The invention is directed toward a string clamp for a tennis racket stringing machine where the string is locked within the clamp between the end of the string clamp which is locked in place and the locking lever. This configuration allows a smaller string clamp to be utilized and also lengthens the life of the string clamp. The string clamp may have shaped feet which fit within channels in a mounting plate in a tennis racket stringing machine. The shaped feet allow the clamp to be removably secured to the mounting plate of the stringing machine when the string clamp is locked.

A down-pressed clamp base includes: a main body having a space and a passage in communication with the space via a connection perforation; a transmission member fitted in the connection perforation; a leverage mechanism including a lever and a link, the link being pivotally connected with the lever and positioned in the passage, a free end of the link being directed to the transmission member; a fastening mechanism disposed in the space; and a string holding mechanism disposed on the main body for holding a racket string. When pressing down the leverage mechanism, the clamp base is fixed on the racket stringer in an operation mode meeting ergonomics. When the leverage mechanism is pressed down, the action forces of the lever, the link and the transmission member fall on the same straight line, whereby the clamp base is fixed on the racket stringer by a fixed fastening force.

A down-pressed clamp base includes: a main body having a space and a passage in communication with the space via a connection perforation; a transmission member fitted in the connection perforation; a leverage mechanism including a lever and a link, the link being pivotally connected with the lever and positioned in the passage, a free end of the link being directed to the transmission member; a fastening mechanism disposed in the space; and a string holding mechanism disposed on the main body for holding a racket string. When pressing down the leverage mechanism, the clamp base is fixed on the racket stringer in an operation mode meeting ergonomics. When the leverage mechanism is pressed down, the action forces of the lever, the link and the transmission member fall on the same straight line, whereby the clamp base is fixed on the racket stringer by a fixed fastening force.

A set of racket cross-string guides which are pre-woven over a string guide holder in the same pattern used for inserting the racket cross-strings.

An automatically braking tensioner for a racket stringing machine is disclosed. The tensioner comprises a tensioner housing, a drum connected to the tensioner housing, a string gripper connected to the drum, a disk brake having an axle extending from an axis of the disc brake, a lever disposed in the tensioner housing, and a brake lever disposed in the tensioner housing. The disk brake is connected to a stringing machine body and is rotably stationary relative to the stringing machine body. As the tensioner is rotated about the disk brake, the brake lever is engaged with the disk brake when the tensioning force is equal to a desired force which can be established my means of a compression spring. In some embodiments the tension can be altered by varying the tension or position of the spring.