A screwdriver is a hand tool used to drive screws and rotate them in their holes. The most common type of screwdriver has a handle with a cylindrical shaft that fits snugly into the head of the screw. The shaft is usually made of metal or plastic and has a tip that is either flat or Phillipshead-shaped. There are also specialty screwdrivers for driving screws with hex head, Torx head, or square drive heads.
The term "number 1 screwdriver" can refer to two different things:
1) It can be used to describe the size of the tip on the screwdriver - specifically, it means that the tip is 3/16 inch wide. This is the most common size of tip found on standard flathead and Phillipshead screwdrivers.
2) It can also be used to describe a specific type of Phillipshead screwdriver known as a "number 1 point." This type of screwdriver has a very thin and pointed tip that is designed for use in tight spaces.