The Mechanic's Grip is one of many ways to comfortably hold a deck of cards.
It is a standard grip utilized primarily by magicians and card cheaters as it allows a sturdy and versatile means by which to hold the cards. Covering the deck with your hand allows you to do things you regularly would not, such as viewing the top card's face (useful in poker or blackjack) or lifting and selecting a card without the spectators knowledge (useful in card tricks). However, it is also the grip taught in many dealer schools around the world.
Refer to the picture at right for finger placements.
To form the Mechanic's Grip, first hold the deck in your hand in the same fashion you might hold a hammer or tool. The cards should be lying flat in your palm with the longer side of the deck lying along the fingers. Take your pointer finger and move it to the short side facing away from you. Take your middle finger, ring finger, and pinkie finger and place them on the long side of the deck. Finally your thumb holds the deck together on the long side opposite of the other fingers. With this grip, more of the deck should be covered by your hand, thus making it more difficult for spectators to see what you are doing.