Emery boards are pieces of cardboard which have emery or emery paper glued to them, making them both abrasive and flexible, used for fingernail and toenail care. They are used by manicurists to shape and smooth the nail during manicure and pedicure sessions. Emery boards are inexpensive and disposable, making them a sanitary alternative to metal nail files.
The nail can be smoothed and shaped accurately by taking light, even strokes in one direction across the top of the nail. Twenty to thirty easy strokes can typically shorten excessively long fingernails, while five to ten strokes are sufficient for shaping the nails.
pitchers and cricket
bowlers have been known to use emery boards to scuff the outside of the ball. This is because, firstly, the roughness can offer more grip and hand control. Secondly, surface scratches also alter the ball's aerodynamics
making it more susceptible to spin and movement when in flight.
However the deliberate manipulation of the ball using an emery board is classed as cheating in Baseball and Cricket.
In an infamous 1987 Major League Baseball incident, Joe Niekro of the Minnesota Twins was caught with an emery board in his pocket and suspended for ten games.