• Ask about the proper fastener at your local hardware store.garysludden/Photodisc/Getty Images
  
  There are several types of fasteners for jobs from auto making to carpentry. Fasteners are intended to connect two things together or attach one thing to a larger item. Screws and bolts are types of fasteners, but there is little distinction between the two. Historically, a bolt was said to have a portion of its shank that was not threaded. This definition has been changed, as it may cause confusion.
  
  

Head

• It would be difficult to determine the difference between a bolt or screw on head alone. Both are defined as a headed, threaded fastener. However, it is the application of force to the head that allows for a distinction. A screw must have torque applied to the head in order to fasten it into stationary material. A bolt, on the other hand, must be held stationary by the head while torque is applied to the bolt's intended fastening.
  
  

Threading

• Threading is also not an exact way to determine bolt from screw. In the past, a distinction was made that screws had external threading winding all the way up to the head. There are currently a number of screw types that do not fit his distinction, yet still meet the other standards of being a screw. Conversely, bolts were defined as being only partially threaded, with a portion of the shaft lacking any threading. As with screws, there are several categories of bolt that no longer meet this qualification.
  
  

Fastening

• Perhaps the main difference between these two fasteners is that of the material in which they will be used. Screws, while being used for a variety of construction materials, must have torque applied to the head in order to thread the fastener into a tapped hole. This tapped hole is a hole that can be formed or created by "self-tapping" screws. So long as the fastening is a hole that is either already there or is being formed by the fastener, it is categorized as a screw. In order to be categorized as a bolt, it must meet the qualification of being threaded into a nut. The head of a bolt is held stationary, while torque is applied to the nut in order to tighten the fastener.
  
  

Confusion

• The confusion occurs when a "bolt" is being threaded into a stationary nut. If torque is not being applied to the nut, then the head of the "bolt" is receiving the applied torque and the nut becomes a stationary tapped hole. This fastener, then, is still considered to be a screw.