To enhance a resilience performance of a ball at hitting the ball, a grommet is configured to include a strip-shaped portion extending in a predetermined direction and a cylindrical portion projecting from one surface of the strip-shaped portion, the cylindrical portion being a portion through which a string passes. A bulge portion is formed on a part on another surface of the strip-shaped portion, the part being along an inner periphery of the cylindrical portion. The bulge portion has a shape bulged more than the other surface of the strip-shaped portion, and the string is folded back at the bulge portion. A plurality of the protrusions are formed between the cylindrical portions adjacent to one another, the plurality of the protrusions being portions to which the string contacts.

The present invention is directed to a racquet design with an inner and outer frame connected by an isolation system. Uniquely adapted to tennis racquets, the natural motion of the inner frame relative to the outer frame upon impact of the tennis ball on the inner frame will generate spin when the ball contacts the inner frame. The relationship between the inner frame, outer frame and isolation system can control the spin imparted to the ball for a given tennis swing. The tuning of the isolators relative to conventional racquet characteristics will increase the amount of ball spin caused by conventional racquets. The invention also increases the accuracy of the tennis ball's trajectory.

A racket frame has an inner thick part (28) having an outer surface (12), an inner surface (14) and a pair of middle surfaces (16) each positioned between the outer surface (12) and the inner surface (14). A thickness (Ti) of the inner surface (14) is greater than a thickness (To) of the outer surface (12). A thickness of the inner thick part (28) gradually increases toward the inside. Consequently, the middle surface (16) is inclined with respect to an X direction. A distance (Ld) between an outer end and an inner end in a thickness direction of the middle surface (16) is equal to or greater than 0.5 mm.

The present invention is directed to a racquet design with an inner and outer frame connected by an isolation system. Uniquely adapted to tennis racquets, the natural motion of the inner frame relative to the outer frame upon impact of the tennis ball on the inner frame will generate spin when the ball contacts the inner frame. The relationship between the inner frame, outer frame and isolation system can control the spin imparted to the ball for a given tennis swing. The tuning of the isolators relative to conventional racquet characteristics will increase the amount of ball spin caused by conventional racquets. The invention also increases the accuracy of the tennis ball's trajectory.