Endorsed by german professional tennis player angelique kerber the yonex vcore si 100 g tennis racket uses yonexs latest technology to produce a racket with great spin and bite the black micro core technology improves stability in the head and reduces vibrations enhancing playability and control over shots the new grommet hole design optimises string movement so spin potential is taken to another level the size of the sweet spot in the head has been increased without reducing control using