Flip belts are compact anti-grav devices which generate a short range negative-gravity field which, when combined with the Harlequins already prodigous [sic?] acrobatic abilities, allows the Harlequins to make all manner of gravity-defying leaps and bounds. Harlequins can ignore difficult terrain – treat difficult terrain as open ground for the purposes of movement. When advancing after winning an assault, or Harlequins can move 3D6 inches instead of 2D6 inches (note that they fall back 2D6 inches as normal). In addition, a Harlequin model may use their full number of Attacks and any specialist close combat weapons they have when within 2" of an enemy in an assault – this is instead of the 1 Attack with no special rules that other models have in this situation. Remember though that models which assault the enemy must try to get into base contact if possible.
Flip Belts
Source: Codex: Harlequins, p. 6