Rule number four?
RULE 4
The Racket
Rackets failing to comply with the following specifications are not approved for play under the Rules of Tennis:
(a) The hitting surface of the rachet shall be flat and consist of a pattern of crossed strings connected to a frame and alternately interlaced or bonded where they cross; and the stringing pattern shall be generally uniform, and in particular not less dense in the center than in any other area. The strings shall be free of attached objects and protrusions other than those utilized solely and specifically to limit or prevent wear and tear or vibration and which are reasonable in size and placement for such purposes.
(b) The frame of the racket shall not exceed 32 inches (81.28cm.) in overall length, including the handle and 12.5 inches (31.75cm.) in overall width. The strung surface shall not exceed 15.5 inches (39.37cm.) in overall length, and 11.5 inches (29.21cm.) in overall width.
(c) The frame, including the handle, shall be free of attached objects and devices other than those utilized solely and specifically to limit or prevent wear and tear or vibration, or to distribute weight. Any objects and devices must be reasonable in size and placement for such purposes.
(d) The frame, including the handle and the strings, shall be free of any device which makes it possible to change materially the shape of the racket, or to change the weight distribution in the direction of the longitudinal axis of the racket which would alter the swing moment of inertia, during the playing of a point.
The International Tennis Federation shall rule on the question of whether any racket or prototype complies with the above specifications or is otherwise approved, or not approved, for play. Such ruling may be undertaken on its own initiative, or upon application by any party with a bona fide interest therein, including any player, equipment manufacturer or National Association or members thereof. Such rulings and applications shall be made in accordance with the applicable Review and Hearing Procedures of the International Tennis Federation, copies of which may be obtained from the office of the Secretary.
Case 1. Can there be more than one set of strings on the hitting surface of a racket?
Decision. No. The rule clearly mentions a pattern, and not patterns, of crossed strings.
Case 2. Is the stringing pattern of a racket considered to be generally uniform and flat if the strings are on more than one plane?
Decision. No.
Case 3. Can a vibration dampening device be placed on the strings of a racket and if so here can it be placed?
Decision. Yes; but such devices may only be placed outside the pattern of crossed